#next contents
W3C
HTML 4.01 Specification
W3C Recommendation 24 December 1999
This version:
http://www.w3.org/TR/1999/REC-html401-19991224
(plain text [794Kb], gzip'ed tar archive of HTML files [371Kb],
a .zip archive of HTML files [405Kb], gzip'ed Postscript file
[746Kb, 389 pages], gzip'ed PDF file [963Kb])
Latest version of HTML 4.01:
http://www.w3.org/TR/html401
Latest version of HTML 4:
http://www.w3.org/TR/html4
Latest version of HTML:
http://www.w3.org/TR/html
Previous version of HTML 4.01:
http://www.w3.org/TR/1999/PR-html40-19990824
Previous HTML 4 Recommendation:
http://www.w3.org/TR/1998/REC-html40-19980424
Editors:
Dave Raggett <dsr@w3.org>
Arnaud Le Hors, W3C
Ian Jacobs, W3C
Copyright ©1997-1999 W3C® (MIT, INRIA, Keio), All Rights Reserved. W3C
liability, trademark, document use and software licensing rules apply.
_________________________________________________________________
Abstract
This specification defines the HyperText Markup Language (HTML), the
publishing language of the World Wide Web. This specification defines
HTML 4.01, which is a subversion of HTML 4. In addition to the text,
multimedia, and hyperlink features of the previous versions of HTML
(HTML 3.2 [HTML32] and HTML 2.0 [RFC1866]), HTML 4 supports more
multimedia options, scripting languages, style sheets, better printing
facilities, and documents that are more accessible to users with
disabilities. HTML 4 also takes great strides towards the
internationalization of documents, with the goal of making the Web
truly World Wide.
HTML 4 is an SGML application conforming to International Standard ISO
8879 -- Standard Generalized Markup Language [ISO8879].
Status of this document
This section describes the status of this document at the time of its
publication. Other documents may supersede this document. The latest
status of this document series is maintained at the W3C.
This document specifies HTML 4.01, which is part of the HTML 4 line of
specifications. The first version of HTML 4 was HTML 4.0 [HTML40],
published on 18 December 1997 and revised 24 April 1998. This
specification is the first HTML 4.01 Recommendation. It includes
non-editorial changes since the 24 April version of HTML 4.0. There
have been some changes to the DTDs, for example. This document
obsoletes previous versions of HTML 4.0, although W3C will continue to
make those specifications and their DTDs available at the W3C Web
site.
This document has been reviewed by W3C Members and other interested
parties and has been endorsed by the Director as a W3C Recommendation.
It is a stable document and may be used as reference material or cited
as a normative reference from another document. W3C's role in making
the Recommendation is to draw attention to the specification and to
promote its widespread deployment. This enhances the functionality and
interoperability of the Web.
W3C recommends that user agents and authors (and in particular,
authoring tools) produce HTML 4.01 documents rather than HTML 4.0
documents. W3C recommends that authors produce HTML 4 documents
instead of HTML 3.2 documents. For reasons of backward compatibility,
W3C also recommends that tools interpreting HTML 4 continue to support
HTML 3.2 and HTML 2.0 as well.
For information about the next generation of HTML, "The Extensible
HyperText Markup Language" [XHTML], please refer to the W3C HTML
Activity and the list of W3C Technical Reports.
This document has been produced as part of the W3C HTML Activity. The
goals of the HTML Working Group (Members only) are discussed in the
HTML Working Group charter (Members only).
A list of current W3C Recommendations and other technical documents
can be found at http://www.w3.org/TR.
Public discussion on HTML features takes place on www-html@w3.org
(archives of www-html@w3.org).
Available languages
The English version of this specification is the only normative
version. However, for translations of this document, see
http://www.w3.org/MarkUp/html4-updates/translations.
Errata
The list of known errors in this specification is available at:
http://www.w3.org/MarkUp/html4-updates/errata
Please report errors in this document to www-html-editor@w3.org.
Quick Table of Contents
1. About the HTML 4 Specification
2. Introduction to HTML 4
3. On SGML and HTML
4. Conformance: requirements and recommendations
5. HTML Document Representation - Character sets, character
encodings, and entities
6. Basic HTML data types - Character data, colors, lengths, URIs,
content types, etc.
7. The global structure of an HTML document - The HEAD and BODY of a
document
8. Language information and text direction - International
considerations for text
9. Text - Paragraphs, Lines, and Phrases
10. Lists - Unordered, Ordered, and Definition Lists
11. Tables
12. Links - Hypertext and Media-Independent Links
13. Objects, Images, and Applets
14. Style Sheets - Adding style to HTML documents
15. Alignment, font styles, and horizontal rules
16. Frames - Multi-view presentation of documents
17. Forms - User-input Forms: Text Fields, Buttons, Menus, and more
18. Scripts - Animated Documents and Smart Forms
19. SGML reference information for HTML - Formal definition of HTML
and validation
20. SGML Declaration of HTML 4
21. Document Type Definition
22. Transitional Document Type Definition
23. Frameset Document Type Definition
24. Character entity references in HTML 4
A. Changes
B. Performance, Implementation, and Design Notes
* References
* Index of Elements
* Index of Attributes
* Index
Full Table of Contents
1. About the HTML 4 Specification
1. How the specification is organized
2. Document conventions
1. Elements and attributes
2. Notes and examples
3. Acknowledgments
1. Acknowledgments for the current revision
4. Copyright Notice
2. Introduction to HTML 4
1. What is the World Wide Web?
1. Introduction to URIs
2. Fragment identifiers
3. Relative URIs
2. What is HTML?
1. A brief history of HTML
3. HTML 4
1. Internationalization
2. Accessibility
3. Tables
4. Compound documents
5. Style sheets
6. Scripting
7. Printing
4. Authoring documents with HTML 4
1. Separate structure and presentation
2. Consider universal accessibility to the Web
3. Help user agents with incremental rendering
3. On SGML and HTML
1. Introduction to SGML
2. SGML constructs used in HTML
1. Elements
2. Attributes
3. Character references
4. Comments
3. How to read the HTML DTD
1. DTD Comments
2. Parameter entity definitions
3. Element declarations
# Content model definitions
4. Attribute declarations
# DTD entities in attribute definitions
# Boolean attributes
4. Conformance: requirements and recommendations
1. Definitions
2. SGML
3. The text/html content type
5. HTML Document Representation - Character sets, character
encodings, and entities
1. The Document Character Set
2. Character encodings
1. Choosing an encoding
# Notes on specific encodings
2. Specifying the character encoding
3. Character references
1. Numeric character references
2. Character entity references
4. Undisplayable characters
6. Basic HTML data types - Character data, colors, lengths, URIs,
content types, etc.
1. Case information
2. SGML basic types
3. Text strings
4. URIs
5. Colors
1. Notes on using colors
6. Lengths
7. Content types (MIME types)
8. Language codes
9. Character encodings
10. Single characters
11. Dates and times
12. Link types
13. Media descriptors
14. Script data
15. Style sheet data
16. Frame target names
7. The global structure of an HTML document - The HEAD and BODY of a
document
1. Introduction to the structure of an HTML document
2. HTML version information
3. The HTML element
4. The document head
1. The HEAD element
2. The TITLE element
3. The title attribute
4. Meta data
# Specifying meta data
# The META element
# Meta data profiles
5. The document body
1. The BODY element
2. Element identifiers: the id and class attributes
3. Block-level and inline elements
4. Grouping elements: the DIV and SPAN elements
5. Headings: The H1, H2, H3, H4, H5, H6 elements
6. The ADDRESS element
8. Language information and text direction - International
considerations for text
1. Specifying the language of content: the lang attribute
1. Language codes
2. Inheritance of language codes
3. Interpretation of language codes
2. Specifying the direction of text and tables: the dir
attribute
1. Introduction to the bidirectional algorithm
2. Inheritance of text direction information
3. Setting the direction of embedded text
4. Overriding the bidirectional algorithm: the BDO element
5. Character references for directionality and joining
control
6. The effect of style sheets on bidirectionality
9. Text - Paragraphs, Lines, and Phrases
1. White space
2. Structured text
1. Phrase elements: EM, STRONG, DFN, CODE, SAMP, KBD, VAR,
CITE, ABBR, and ACRONYM
2. Quotations: The BLOCKQUOTE and Q elements
# Rendering quotations
3. Subscripts and superscripts: the SUB and SUP elements
3. Lines and Paragraphs
1. Paragraphs: the P element
2. Controlling line breaks
# Forcing a line break: the BR element
# Prohibiting a line break
3. Hyphenation
4. Preformatted text: The PRE element
5. Visual rendering of paragraphs
4. Marking document changes: The INS and DEL elements
10. Lists - Unordered, Ordered, and Definition Lists
1. Introduction to lists
2. Unordered lists (UL), ordered lists (OL), and list items (LI)
3. Definition lists: the DL, DT, and DD elements
1. Visual rendering of lists
4. The DIR and MENU elements
11. Tables
1. Introduction to tables
2. Elements for constructing tables
1. The TABLE element
# Table directionality
2. Table Captions: The CAPTION element
3. Row groups: the THEAD, TFOOT, and TBODY elements
4. Column groups: the COLGROUP and COL elements
# The COLGROUP element
# The COL element
# Calculating the number of columns in a table
# Calculating the width of columns
5. Table rows: The TR element
6. Table cells: The TH and TD elements
# Cells that span several rows or columns
3. Table formatting by visual user agents
1. Borders and rules
2. Horizontal and vertical alignment
# Inheritance of alignment specifications
3. Cell margins
4. Table rendering by non-visual user agents
1. Associating header information with data cells
2. Categorizing cells
3. Algorithm to find heading information
5. Sample table
12. Links - Hypertext and Media-Independent Links
1. Introduction to links and anchors
1. Visiting a linked resource
2. Other link relationships
3. Specifying anchors and links
4. Link titles
5. Internationalization and links
2. The A element
1. Syntax of anchor names
2. Nested links are illegal
3. Anchors with the id attribute
4. Unavailable and unidentifiable resources
3. Document relationships: the LINK element
1. Forward and reverse links
2. Links and external style sheets
3. Links and search engines
4. Path information: the BASE element
1. Resolving relative URIs
13. Objects, Images, and Applets
1. Introduction to objects, images, and applets
2. Including an image: the IMG element
3. Generic inclusion: the OBJECT element
1. Rules for rendering objects
2. Object initialization: the PARAM element
3. Global naming schemes for objects
4. Object declarations and instantiations
4. Including an applet: the APPLET element
5. Notes on embedded documents
6. Image maps
1. Client-side image maps: the MAP and AREA elements
# Client-side image map examples
2. Server-side image maps
7. Visual presentation of images, objects, and applets
1. Width and height
2. White space around images and objects
3. Borders
4. Alignment
8. How to specify alternate text
14. Style Sheets - Adding style to HTML documents
1. Introduction to style sheets
2. Adding style to HTML
1. Setting the default style sheet language
2. Inline style information
3. Header style information: the STYLE element
4. Media types
3. External style sheets
1. Preferred and alternate style sheets
2. Specifying external style sheets
4. Cascading style sheets
1. Media-dependent cascades
2. Inheritance and cascading
5. Hiding style data from user agents
6. Linking to style sheets with HTTP headers
15. Alignment, font styles, and horizontal rules
1. Formatting
1. Background color
2. Alignment
3. Floating objects
# Float an object
# Float text around an object
2. Fonts
1. Font style elements: the TT, I, B, BIG, SMALL, STRIKE,
S, and U elements
2. Font modifier elements: FONT and BASEFONT
3. Rules: the HR element
16. Frames - Multi-view presentation of documents
1. Introduction to frames
2. Layout of frames
1. The FRAMESET element
# Rows and columns
# Nested frame sets
# Sharing data among frames
2. The FRAME element
# Setting the initial contents of a frame
# Visual rendering of a frame
3. Specifying target frame information
1. Setting the default target for links
2. Target semantics
4. Alternate content
1. The NOFRAMES element
2. Long descriptions of frames
5. Inline frames: the IFRAME element
17. Forms - User-input Forms: Text Fields, Buttons, Menus, and more
1. Introduction to forms
2. Controls
1. Control types
3. The FORM element
4. The INPUT element
1. Control types created with INPUT
2. Examples of forms containing INPUT controls
5. The BUTTON element
6. The SELECT, OPTGROUP, and OPTION elements
1. Pre-selected options
7. The TEXTAREA element
8. The ISINDEX element
9. Labels
1. The LABEL element
10. Adding structure to forms: the FIELDSET and LEGEND elements
11. Giving focus to an element
1. Tabbing navigation
2. Access keys
12. Disabled and read-only controls
1. Disabled controls
2. Read-only controls
13. Form submission
1. Form submission method
2. Successful controls
3. Processing form data
# Step one: Identify the successful controls
# Step two: Build a form data set
# Step three: Encode the form data set
# Step four: Submit the encoded form data set
4. Form content types
# application/x-www-form-urlencoded
# multipart/form-data
18. Scripts - Animated Documents and Smart Forms
1. Introduction to scripts
2. Designing documents for user agents that support scripting
1. The SCRIPT element
2. Specifying the scripting language
# The default scripting language
# Local declaration of a scripting language
# References to HTML elements from a script
3. Intrinsic events
4. Dynamic modification of documents
3. Designing documents for user agents that don't support
scripting
1. The NOSCRIPT element
2. Hiding script data from user agents
19. SGML reference information for HTML - Formal definition of HTML
and validation
1. Document Validation
2. Sample SGML catalog
20. SGML Declaration of HTML 4
1. SGML Declaration
21. Document Type Definition
22. Transitional Document Type Definition
23. Frameset Document Type Definition
24. Character entity references in HTML 4
1. Introduction to character entity references
2. Character entity references for ISO 8859-1 characters
1. The list of characters
3. Character entity references for symbols, mathematical
symbols, and Greek letters
1. The list of characters
4. Character entity references for markup-significant and
internationalization characters
1. The list of characters
A. Changes
1. Changes between 24 April 1998 HTML 4.0 and 24 December 1999
HTML 4.01 versions
1. Changes to the specification
# General changes
# On SGML and HTML
# HTML Document Representation
# Basic HTML data types
# Global structure of an HTML document
# Language information and text direction
# Tables
# Links
# Objects, Images, and Applets
# Style Sheets in HTML Documents
# Frames
# Forms
# SGML Declaration
# Strict DTD
# Notes
# References
2. Errors that were corrected
3. Minor typographical errors that were corrected
4. Clarifications
5. Known Browser problems
2. Changes between 18 December 1997 and 24 April 1998 versions
1. Errors that were corrected
2. Minor typographical errors that were corrected
3. Changes between HTML 3.2 and HTML 4.0 (18 December 1997)
1. Changes to elements
# New elements
# Deprecated elements
# Obsolete elements
2. Changes to attributes
3. Changes for accessibility
4. Changes for meta data
5. Changes for text
6. Changes for links
7. Changes for tables
8. Changes for images, objects, and image maps
9. Changes for forms
10. Changes for style sheets
11. Changes for frames
12. Changes for scripting
13. Changes for internationalization
B. Performance, Implementation, and Design Notes
1. Notes on invalid documents
2. Special characters in URI attribute values
1. Non-ASCII characters in URI attribute values
2. Ampersands in URI attribute values
3. SGML implementation notes
1. Line breaks
2. Specifying non-HTML data
# Element content
# Attribute values
3. SGML features with limited support
4. Boolean attributes
5. Marked Sections
6. Processing Instructions
7. Shorthand markup
4. Notes on helping search engines index your Web site
1. Search robots
# The robots.txt file
# Robots and the META element
5. Notes on tables
1. Design rationale
# Dynamic reformatting
# Incremental display
# Structure and presentation
# Row and column groups
# Accessibility
2. Recommended Layout Algorithms
# Fixed Layout Algorithm
# Autolayout Algorithm
6. Notes on forms
1. Incremental display
2. Future projects
7. Notes on scripting
1. Reserved syntax for future script macros
# Current Practice for Script Macros
8. Notes on frames
9. Notes on accessibility
10. Notes on security
1. Security issues for forms
* References
1. Normative references
2. Informative references
* Index of Elements
* Index of Attributes
* Index
1 About the HTML 4 Specification
Contents
1. How the specification is organized
2. Document conventions
1. Elements and attributes
2. Notes and examples
3. Acknowledgments
1. Acknowledgments for the current revision
4. Copyright Notice
1.1 How the specification is organized
This specification is divided into the following sections:
Sections 2 and 3: Introduction to HTML 4
The introduction describes HTML's place in the scheme of the
World Wide Web, provides a brief history of the development of
HTML, highlights what can be done with HTML 4, and provides
some HTML authoring tips.
The brief SGML tutorial gives readers some understanding of
HTML's relationship to SGML and gives summary information on
how to read the HTML Document Type Definition (DTD).
Sections 4 - 24: HTML 4 reference manual
The bulk of the reference manual consists of the HTML language
reference, which defines all elements and attributes of the
language.
This document has been organized by topic rather than by the
grammar of HTML. Topics are grouped into three categories:
structure, presentation, and interactivity. Although it is not
easy to divide HTML constructs perfectly into these three
categories, the model reflects the HTML Working Group's
experience that separating a document's structure from its
presentation produces more effective and maintainable
documents.
The language reference consists of the following information:
+ What characters may appear in an HTML document.
+ Basic data types of an HTML document.
+ Elements that govern the structure of an HTML document,
including text, lists, tables, links, and included objects,
images, and applets.
+ Elements that govern the presentation of an HTML document,
including style sheets, fonts, colors, rules, and other
visual presentation, and frames for multi-windowed
presentations.
+ Elements that govern interactivity with an HTML document,
including forms for user input and scripts for active
documents.
+ The SGML formal definition of HTML:
o The SGML declaration of HTML.
o Three DTDs: strict, transitional, and frameset.
o The list of character references.
Appendixes
The first appendix contains information about changes from HTML
3.2 to help authors and implementors with the transition to
HTML 4, and changes from the 18 December 1997 specification.
The second appendix contains performance and implementation
notes, and is primarily intended to help implementors create
user agents for HTML 4.
References
A list of normative and informative references.
Indexes
Three indexes give readers rapid access to the definition of
key concepts, elements and attributes.
1.2 Document conventions
This document has been written with two types of readers in mind:
authors and implementors. We hope the specification will provide
authors with the tools they need to write efficient, attractive, and
accessible documents, without over-exposing them to HTML's
implementation details. Implementors, however, should find all they
need to build conforming user agents.
The specification may be approached in several ways:
* Read from beginning to end. The specification begins with a
general presentation of HTML and becomes more and more technical
and specific towards the end.
* Quick access to information. In order to get information about
syntax and semantics as quickly as possible, the online version of
the specification includes the following features:
1. Every reference to an element or attribute is linked to its
definition in the specification. Each element or attribute is
defined in only one location.
2. Every page includes links to the indexes, so you never are
more than two links away from finding the definition of an
element or attribute.
3. The front pages of each section of the language reference
manual extend the initial table of contents with more detail
about that section.
1.2.1 Elements and attributes
Element names are written in uppercase letters (e.g., BODY). Attribute
names are written in lowercase letters (e.g., lang, onsubmit). Recall
that in HTML, element and attribute names are case-insensitive; the
convention is meant to encourage readability.
Element and attribute names in this document have been marked up and
may be rendered specially by some user agents.
Each attribute definition specifies the type of its value. If the type
allows a small set of possible values, the definition lists the set of
values, separated by a bar (|).
After the type information, each attribute definition indicates the
case-sensitivity of its values, between square brackets ("[]"). See
the section on case information for details.
1.2.2 Notes and examples
Informative notes are emphasized to stand out from surrounding text
and may be rendered specially by some user agents.
All examples illustrating deprecated usage are marked as "DEPRECATED
EXAMPLE". Deprecated examples also include recommended alternate
solutions. All examples that illustrates illegal usage are clearly
marked "ILLEGAL EXAMPLE".
Examples and notes have been marked up and may be rendered specially
by some user agents.
1.3 Acknowledgments
Thanks to everyone who has helped to author the working drafts that
went into the HTML 4 specification, and to all those who have sent
suggestions and corrections.
Many thanks to the Web Accessibility Initiative task force (WAI HC
group) for their work on improving the accessibility of HTML and to
T.V. Raman (Adobe) for his early work on developing accessible forms.
The authors of this specification, the members of the W3C HTML Working
Group, deserve much applause for their diligent review of this
document, their constructive comments, and their hard work: John D.
Burger (MITRE), Steve Byrne (JavaSoft), Martin J. Dürst (University of
Zurich), Daniel Glazman (Electricité de France), Scott Isaacs
(Microsoft), Murray Maloney (GRIF), Steven Pemberton (CWI), Robert
Pernett (Lotus), Jared Sorensen (Novell), Powell Smith (IBM), Robert
Stevahn (HP), Ed Tecot (Microsoft), Jeffrey Veen (HotWired), Mike
Wexler (Adobe), Misha Wolf (Reuters), and Lauren Wood (SoftQuad).
Thank you Dan Connolly (W3C) for rigorous and bountiful input as
part-time editor and thoughtful guidance as chairman of the HTML
Working Group. Thank you Sally Khudairi (W3C) for your indispensable
work on press releases.
Thanks to David M. Abrahamson and Roger Price for their careful
reading of the specification and constructive comments.
Thanks to Jan Kärrman, author of html2ps for helping so much in
creating the Postscript version of the specification.
Of particular help from the W3C at Sophia-Antipolis were Janet Bertot,
Bert Bos, Stephane Boyera, Daniel Dardailler, Yves Lafon, Håkon Lie,
Chris Lilley, and Colas Nahaboo (Bull).
Lastly, thanks to Tim Berners-Lee without whom none of this would have
been possible.
1.3.1 Acknowledgments for the current revision
Many thanks to Shane McCarron for tracking errata for this revision of
the specification.
1.4 Copyright Notice
For information about copyrights, please refer to the W3C Intellectual
Property Notice, the W3C Document Notice, and the W3C IPR Software
Notice.
2 Introduction to HTML 4
Contents
1. What is the World Wide Web?
1. Introduction to URIs
2. Fragment identifiers
3. Relative URIs
2. What is HTML?
1. A brief history of HTML
3. HTML 4
1. Internationalization
2. Accessibility
3. Tables
4. Compound documents
5. Style sheets
6. Scripting
7. Printing
4. Authoring documents with HTML 4
1. Separate structure and presentation
2. Consider universal accessibility to the Web
3. Help user agents with incremental rendering
2.1 What is the World Wide Web?
The World Wide Web (Web) is a network of information resources. The
Web relies on three mechanisms to make these resources readily
available to the widest possible audience:
1. A uniform naming scheme for locating resources on the Web (e.g.,
URIs).
2. Protocols, for access to named resources over the Web (e.g.,
HTTP).
3. Hypertext, for easy navigation among resources (e.g., HTML).
The ties between the three mechanisms are apparent throughout this
specification.
2.1.1 Introduction to URIs
Every resource available on the Web -- HTML document, image, video
clip, program, etc. -- has an address that may be encoded by a
Universal Resource Identifier, or "URI".
URIs typically consist of three pieces:
1. The naming scheme of the mechanism used to access the resource.
2. The name of the machine hosting the resource.
3. The name of the resource itself, given as a path.
Consider the URI that designates the W3C Technical Reports page:
http://www.w3.org/TR
This URI may be read as follows: There is a document available via the
HTTP protocol (see [RFC2616]), residing on the machine www.w3.org,
accessible via the path "/TR". Other schemes you may see in HTML
documents include "mailto" for email and "ftp" for FTP.
Here is another example of a URI. This one refers to a user's mailbox:
...this is text...
For all comments, please send email to
<A href="mailto:joe@someplace.com">Joe Cool</A>.
Note. Most readers may be familiar with the term "URL" and not the
term "URI". URLs form a subset of the more general URI naming scheme.
2.1.2 Fragment identifiers
Some URIs refer to a location within a resource. This kind of URI ends
with "#" followed by an anchor identifier (called the fragment
identifier). For instance, here is a URI pointing to an anchor named
section_2:
http://somesite.com/html/top.html#section_2
2.1.3 Relative URIs
A relative URI doesn't contain any naming scheme information. Its path
generally refers to a resource on the same machine as the current
document. Relative URIs may contain relative path components (e.g.,
".." means one level up in the hierarchy defined by the path), and may
contain fragment identifiers.
Relative URIs are resolved to full URIs using a base URI. As an
example of relative URI resolution, assume we have the base URI
"http://www.acme.com/support/intro.html". The relative URI in the
following markup for a hypertext link:
<A href="suppliers.html">Suppliers</A>
would expand to the full URI
"http://www.acme.com/support/suppliers.html", while the relative URI
in the following markup for an image
<IMG src="../icons/logo.gif" alt="logo">
would expand to the full URI "http://www.acme.com/icons/logo.gif".
In HTML, URIs are used to:
* Link to another document or resource, (see the A and LINK
elements).
* Link to an external style sheet or script (see the LINK and SCRIPT
elements).
* Include an image, object, or applet in a page, (see the IMG,
OBJECT, APPLET and INPUT elements).
* Create an image map (see the MAP and AREA elements).
* Submit a form (see FORM).
* Create a frame document (see the FRAME and IFRAME elements).
* Cite an external reference (see the Q, BLOCKQUOTE, INS and DEL
elements).
* Refer to metadata conventions describing a document (see the HEAD
element).
Please consult the section on the URI type for more information about
URIs.
2.2 What is HTML?
To publish information for global distribution, one needs a
universally understood language, a kind of publishing mother tongue
that all computers may potentially understand. The publishing language
used by the World Wide Web is HTML (from HyperText Markup Language).
HTML gives authors the means to:
* Publish online documents with headings, text, tables, lists,
photos, etc.
* Retrieve online information via hypertext links, at the click of a
button.
* Design forms for conducting transactions with remote services, for
use in searching for information, making reservations, ordering
products, etc.
* Include spread-sheets, video clips, sound clips, and other
applications directly in their documents.
2.2.1 A brief history of HTML
HTML was originally developed by Tim Berners-Lee while at CERN, and
popularized by the Mosaic browser developed at NCSA. During the course
of the 1990s it has blossomed with the explosive growth of the Web.
During this time, HTML has been extended in a number of ways. The Web
depends on Web page authors and vendors sharing the same conventions
for HTML. This has motivated joint work on specifications for HTML.
HTML 2.0 (November 1995, see [RFC1866]) was developed under the aegis
of the Internet Engineering Task Force (IETF) to codify common
practice in late 1994. HTML+ (1993) and HTML 3.0 (1995, see [HTML30])
proposed much richer versions of HTML. Despite never receiving
consensus in standards discussions, these drafts led to the adoption
of a range of new features. The efforts of the World Wide Web
Consortium's HTML Working Group to codify common practice in 1996
resulted in HTML 3.2 (January 1997, see [HTML32]). Changes from HTML
3.2 are summarized in Appendix A
Most people agree that HTML documents should work well across
different browsers and platforms. Achieving interoperability lowers
costs to content providers since they must develop only one version of
a document. If the effort is not made, there is much greater risk that
the Web will devolve into a proprietary world of incompatible formats,
ultimately reducing the Web's commercial potential for all
participants.
Each version of HTML has attempted to reflect greater consensus among
industry players so that the investment made by content providers will
not be wasted and that their documents will not become unreadable in a
short period of time.
HTML has been developed with the vision that all manner of devices
should be able to use information on the Web: PCs with graphics
displays of varying resolution and color depths, cellular telephones,
hand held devices, devices for speech for output and input, computers
with high or low bandwidth, and so on.
2.3 HTML 4
HTML 4 extends HTML with mechanisms for style sheets, scripting,
frames, embedding objects, improved support for right to left and
mixed direction text, richer tables, and enhancements to forms,
offering improved accessibility for people with disabilities.
HTML 4.01 is a revision of HTML 4.0 that corrects errors and makes
some changes since the previous revision.
2.3.1 Internationalization
This version of HTML has been designed with the help of experts in the
field of internationalization, so that documents may be written in
every language and be transported easily around the world. This has
been accomplished by incorporating [RFC2070], which deals with the
internationalization of HTML.
One important step has been the adoption of the ISO/IEC:10646 standard
(see [ISO10646]) as the document character set for HTML. This is the
world's most inclusive standard dealing with issues of the
representation of international characters, text direction,
punctuation, and other world language issues.
HTML now offers greater support for diverse human languages within a
document. This allows for more effective indexing of documents for
search engines, higher-quality typography, better text-to-speech
conversion, better hyphenation, etc.
2.3.2 Accessibility
As the Web community grows and its members diversify in their
abilities and skills, it is crucial that the underlying technologies
be appropriate to their specific needs. HTML has been designed to make
Web pages more accessible to those with physical limitations. HTML 4
developments inspired by concerns for accessibility include:
* Better distinction between document structure and presentation,
thus encouraging the use of style sheets instead of HTML
presentation elements and attributes.
* Better forms, including the addition of access keys, the ability
to group form controls semantically, the ability to group SELECT
options semantically, and active labels.
* The ability to markup a text description of an included object
(with the OBJECT element).
* A new client-side image map mechanism (the MAP element) that
allows authors to integrate image and text links.
* The requirement that alternate text accompany images included with
the IMG element and image maps included with the AREA element.
* Support for the title and lang attributes on all elements.
* Support for the ABBR and ACRONYM elements.
* A wider range of target media (tty, braille, etc.) for use with
style sheets.
* Better tables, including captions, column groups, and mechanisms
to facilitate non-visual rendering.
* Long descriptions of tables, images, frames, etc.
Authors who design pages with accessibility issues in mind will not
only receive the blessings of the accessibility community, but will
benefit in other ways as well: well-designed HTML documents that
distinguish structure and presentation will adapt more easily to new
technologies.
Note. For more information about designing accessible HTML documents,
please consult [WAI].
2.3.3 Tables
The new table model in HTML is based on [RFC1942]. Authors now have
greater control over structure and layout (e.g., column groups). The
ability of designers to recommend column widths allows user agents to
display table data incrementally (as it arrives) rather than waiting
for the entire table before rendering.
Note. At the time of writing, some HTML authoring tools rely
extensively on tables for formatting, which may easily cause
accessibility problems.
2.3.4 Compound documents
HTML now offers a standard mechanism for embedding generic media
objects and applications in HTML documents. The OBJECT element
(together with its more specific ancestor elements IMG and APPLET)
provides a mechanism for including images, video, sound, mathematics,
specialized applications, and other objects in a document. It also
allows authors to specify a hierarchy of alternate renderings for user
agents that don't support a specific rendering.
2.3.5 Style sheets
Style sheets simplify HTML markup and largely relieve HTML of the
responsibilities of presentation. They give both authors and users
control over the presentation of documents -- font information,
alignment, colors, etc.
Style information can be specified for individual elements or groups
of elements. Style information may be specified in an HTML document or
in external style sheets.
The mechanisms for associating a style sheet with a document is
independent of the style sheet language.
Before the advent of style sheets, authors had limited control over
rendering. HTML 3.2 included a number of attributes and elements
offering control over alignment, font size, and text color. Authors
also exploited tables and images as a means for laying out pages. The
relatively long time it takes for users to upgrade their browsers
means that these features will continue to be used for some time.
However, since style sheets offer more powerful presentation
mechanisms, the World Wide Web Consortium will eventually phase out
many of HTML's presentation elements and attributes. Throughout the
specification elements and attributes at risk are marked as
"deprecated". They are accompanied by examples of how to achieve the
same effects with other elements or style sheets.
2.3.6 Scripting
Through scripts, authors may create dynamic Web pages (e.g., "smart
forms" that react as users fill them out) and use HTML as a means to
build networked applications.
The mechanisms provided to include scripts in an HTML document are
independent of the scripting language.
2.3.7 Printing
Sometimes, authors will want to make it easy for users to print more
than just the current document. When documents form part of a larger
work, the relationships between them can be described using the HTML
LINK element or using W3C's Resource Description Framework (RDF) (see
[RDF10]).
2.4 Authoring documents with HTML 4
We recommend that authors and implementors observe the following
general principles when working with HTML 4.
2.4.1 Separate structure and presentation
HTML has its roots in SGML which has always been a language for the
specification of structural markup. As HTML matures, more and more of
its presentational elements and attributes are being replaced by other
mechanisms, in particular style sheets. Experience has shown that
separating the structure of a document from its presentational aspects
reduces the cost of serving a wide range of platforms, media, etc.,
and facilitates document revisions.
2.4.2 Consider universal accessibility to the Web
To make the Web more accessible to everyone, notably those with
disabilities, authors should consider how their documents may be
rendered on a variety of platforms: speech-based browsers,
braille-readers, etc. We do not recommend that authors limit their
creativity, only that they consider alternate renderings in their
design. HTML offers a number of mechanisms to this end (e.g., the alt
attribute, the accesskey attribute, etc.)
Furthermore, authors should keep in mind that their documents may be
reaching a far-off audience with different computer configurations. In
order for documents to be interpreted correctly, authors should
include in their documents information about the natural language and
direction of the text, how the document is encoded, and other issues
related to internationalization.
2.4.3 Help user agents with incremental rendering
By carefully designing their tables and making use of new table
features in HTML 4, authors can help user agents render documents more
quickly. Authors can learn how to design tables for incremental
rendering (see the TABLE element). Implementors should consult the
notes on tables in the appendix for information on incremental
algorithms.
3 On SGML and HTML
Contents
1. Introduction to SGML
2. SGML constructs used in HTML
1. Elements
2. Attributes
3. Character references
4. Comments
3. How to read the HTML DTD
1. DTD Comments
2. Parameter entity definitions
3. Element declarations
o Content model definitions
4. Attribute declarations
o DTD entities in attribute definitions
o Boolean attributes
This section of the document introduces SGML and discusses its
relationship to HTML. A complete discussion of SGML is left to the
standard (see [ISO8879]).
3.1 Introduction to SGML
SGML is a system for defining markup languages. Authors mark up their
documents by representing structural, presentational, and semantic
information alongside content. HTML is one example of a markup
language. Here is an example of an HTML document:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>My first HTML document</TITLE>
</HEAD>
<BODY>
<P>Hello world!
</BODY>
</HTML>
An HTML document is divided into a head section (here, between <HEAD>
and </HEAD>) and a body (here, between <BODY> and </BODY>). The title
of the document appears in the head (along with other information
about the document), and the content of the document appears in the
body. The body in this example contains just one paragraph, marked up
with <P>.
Each markup language defined in SGML is called an SGML application. An
SGML application is generally characterized by:
1. An SGML declaration. The SGML declaration specifies which
characters and delimiters may appear in the application.
2. A document type definition (DTD). The DTD defines the syntax of
markup constructs. The DTD may include additional definitions such
as character entity references.
3. A specification that describes the semantics to be ascribed to the
markup. This specification also imposes syntax restrictions that
cannot be expressed within the DTD.
4. Document instances containing data (content) and markup. Each
instance contains a reference to the DTD to be used to interpret
it.
This specification includes an SGML declaration, three document type
definitions (see the section on HTML version information for a
description of the three), and a list of character references.
3.2 SGML constructs used in HTML
The following sections introduce SGML constructs that are used in
HTML.
The appendix lists some SGML features that are not widely supported by
HTML tools and user agents and should be avoided.
3.2.1 Elements
An SGML document type definition declares element types that represent
structures or desired behavior. HTML includes element types that
represent paragraphs, hypertext links, lists, tables, images, etc.
Each element type declaration generally describes three parts: a start
tag, content, and an end tag.
The element's name appears in the start tag (written <element-name>)
and the end tag (written </element-name>); note the slash before the
element name in the end tag. For example, the start and end tags of
the UL element type delimit the items in a list:
<UL>
<LI><P>...list item 1...
<LI><P>...list item 2...
</UL>
Some HTML element types allow authors to omit end tags (e.g., the P
and LI element types). A few element types also allow the start tags
to be omitted; for example, HEAD and BODY. The HTML DTD indicates for
each element type whether the start tag and end tag are required.
Some HTML element types have no content. For example, the line break
element BR has no content; its only role is to terminate a line of
text. Such empty elements never have end tags. The document type
definition and the text of the specification indicate whether an
element type is empty (has no content) or, if it can have content,
what is considered legal content.
Element names are always case-insensitive.
Please consult the SGML standard for information about rules governing
elements (e.g., they must be properly nested, an end tag closes, back
to the matching start tag, all unclosed intervening start tags with
omitted end tags (section 7.5.1), etc.).
For example, the following paragraph:
<P>This is the first paragraph.</P>
...a block element...
may be rewritten without its end tag:
<P>This is the first paragraph.
...a block element...
since the <P> start tag is closed by the following block element.
Similarly, if a paragraph is enclosed by a block element, as in:
<DIV>
<P>This is the paragraph.
</DIV>
the end tag of the enclosing block element (here, </DIV>) implies the
end tag of the open <P> start tag.
Elements are not tags. Some people refer to elements as tags (e.g.,
"the P tag"). Remember that the element is one thing, and the tag (be
it start or end tag) is another. For instance, the HEAD element is
always present, even though both start and end HEAD tags may be
missing in the markup.
All the element types declared in this specification are listed in the
element index.
3.2.2 Attributes
Elements may have associated properties, called attributes, which may
have values (by default, or set by authors or scripts).
Attribute/value pairs appear before the final ">" of an element's
start tag. Any number of (legal) attribute value pairs, separated by
spaces, may appear in an element's start tag. They may appear in any
order.
In this example, the id attribute is set for an H1 element:
<H1 id="section1">
This is an identified heading thanks to the id attribute
</H1>
By default, SGML requires that all attribute values be delimited using
either double quotation marks (ASCII decimal 34) or single quotation
marks (ASCII decimal 39). Single quote marks can be included within
the attribute value when the value is delimited by double quote marks,
and vice versa. Authors may also use numeric character references to
represent double quotes (") and single quotes ('). For double
quotes authors can also use the character entity reference ".
In certain cases, authors may specify the value of an attribute
without any quotation marks. The attribute value may only contain
letters (a-z and A-Z), digits (0-9), hyphens (ASCII decimal 45),
periods (ASCII decimal 46), underscores (ASCII decimal 95), and colons
(ASCII decimal 58). We recommend using quotation marks even when it is
possible to eliminate them.
Attribute names are always case-insensitive.
Attribute values are generally case-insensitive. The definition of
each attribute in the reference manual indicates whether its value is
case-insensitive.
All the attributes defined by this specification are listed in the
attribute index.
3.2.3 Character references
Character references are numeric or symbolic names for characters that
may be included in an HTML document. They are useful for referring to
rarely used characters, or those that authoring tools make it
difficult or impossible to enter. You will see character references
throughout this document; they begin with a "&" sign and end with a
semi-colon (;). Some common examples include:
* "<" represents the < sign.
* ">" represents the > sign.
* """ represents the " mark.
* "å" (in decimal) represents the letter "a" with a small
circle above it.
* "И" (in decimal) represents the Cyrillic capital letter "I".
* "水" (in hexadecimal) represents the Chinese character for
water.
We discuss HTML character references in detail later in the section on
the HTML document character set. The specification also contains a
list of character references that may appear in HTML 4 documents.
3.2.4 Comments
HTML comments have the following syntax:
<!-- this is a comment -->
<!-- and so is this one,
which occupies more than one line -->
White space is not permitted between the markup declaration open
delimiter("<!") and the comment open delimiter ("--"), but is
permitted between the comment close delimiter ("--") and the markup
declaration close delimiter (">"). A common error is to include a
string of hyphens ("---") within a comment. Authors should avoid
putting two or more adjacent hyphens inside comments.
Information that appears between comments has no special meaning
(e.g., character references are not interpreted as such).
Note that comments are markup.
3.3 How to read the HTML DTD
Each element and attribute declaration in this specification is
accompanied by its document type definition fragment. We have chosen
to include the DTD fragments in the specification rather than seek a
more approachable, but longer and less precise means of describing an
element's properties. The following tutorial should allow readers
unfamiliar with SGML to read the DTD and understand the technical
details of the HTML specification.
3.3.1 DTD Comments
In DTDs, comments may spread over one or more lines. In the DTD,
comments are delimited by a pair of "--" marks, e.g.
<!ELEMENT PARAM - O EMPTY -- named property value -->
Here, the comment "named property value" explains the use of the PARAM
element type. Comments in the DTD are informative only.
3.3.2 Parameter entity definitions
The HTML DTD begins with a series of parameter entity definitions. A
parameter entity definition defines a kind of macro that may be
referenced and expanded elsewhere in the DTD. These macros may not
appear in HTML documents, only in the DTD. Other types of macros,
called character references, may be used in the text of an HTML
document or within attribute values.
When the parameter entity is referred to by name in the DTD, it is
expanded into a string.
A parameter entity definition begins with the keyword <!ENTITY %
followed by the entity name, the quoted string the entity expands to,
and finally a closing >. Instances of parameter entities in a DTD
begin with "%", then the parameter entity name, and terminated by an
optional ";".
The following example defines the string that the "%fontstyle;" entity
will expand to.
<!ENTITY % fontstyle "TT | I | B | BIG | SMALL">
The string the parameter entity expands to may contain other parameter
entity names. These names are expanded recursively. In the following
example, the "%inline;" parameter entity is defined to include the
"%fontstyle;", "%phrase;", "%special;" and "%formctrl;" parameter
entities.
<!ENTITY % inline "#PCDATA | %fontstyle; | %phrase; | %special; | %formctrl;">
You will encounter two DTD entities frequently in the HTML DTD:
"%block;" "%inline;". They are used when the content model includes
block-level and inline elements, respectively (defined in the section
on the global structure of an HTML document).
3.3.3 Element declarations
The bulk of the HTML DTD consists of the declarations of element types
and their attributes. The <!ELEMENT keyword begins a declaration and
the > character ends it. Between these are specified:
1. The element's name.
2. Whether the element's tags are optional. Two hyphens that appear
after the element name mean that the start and end tags are
mandatory. One hyphen followed by the letter "O" indicates that
the end tag can be omitted. A pair of letter "O"s indicate that
both the start and end tags can be omitted.
3. The element's content, if any. The allowed content for an element
is called its content model. Element types that are designed to
have no content are called empty elements. The content model for
such element types is declared using the keyword "EMPTY".
In this example:
<!ELEMENT UL - - (LI)+>
* The element type being declared is UL.
* The two hyphens indicate that both the start tag <UL> and the end
tag </UL> for this element type are required.
* The content model for this element type is declared to be "at
least one LI element". Below, we explain how to specify content
models.
This example illustrates the declaration of an empty element type:
<!ELEMENT IMG - O EMPTY>
* The element type being declared is IMG.
* The hyphen and the following "O" indicate that the end tag can be
omitted, but together with the content model "EMPTY", this is
strengthened to the rule that the end tag must be omitted.
* The "EMPTY" keyword means that instances of this type must not
have content.
Content model definitions
The content model describes what may be contained by an instance of an
element type. Content model definitions may include:
* The names of allowed or forbidden element types (e.g., the UL
element contains instances of the LI element type, and the P
element type may not contain other P elements).
* DTD entities (e.g., the LABEL element contains instances of the
"%inline;" parameter entity).
* Document text (indicated by the SGML construct "#PCDATA"). Text
may contain character references. Recall that these begin with &
and end with a semicolon (e.g., "Hergé's adventures of
Tintin" contains the character entity reference for the "e acute"
character).
The content model of an element is specified with the following
syntax. Please note that the list below is a simplification of the
full SGML syntax rules and does not address, e.g., precedences.
( ... )
Delimits a group.
A
A must occur, one time only.
A+
A must occur one or more times.
A?
A must occur zero or one time.
A*
A may occur zero or more times.
+(A)
A may occur.
-(A)
A must not occur.
A | B
Either A or B must occur, but not both.
A , B
Both A and B must occur, in that order.
A & B
Both A and B must occur, in any order.
Here are some examples from the HTML DTD:
<!ELEMENT UL - - (LI)+>
The UL element must contain one or more LI elements.
<!ELEMENT DL - - (DT|DD)+>
The DL element must contain one or more DT or DD elements in any
order.
<!ELEMENT OPTION - O (#PCDATA)>
The OPTION element may only contain text and entities, such as &
-- this is indicated by the SGML data type #PCDATA.
A few HTML element types use an additional SGML feature to exclude
elements from their content model. Excluded elements are preceded by a
hyphen. Explicit exclusions override permitted elements.
In this example, the -(A) signifies that the element A cannot appear
in another A element (i.e., anchors may not be nested).
<!ELEMENT A - - (%inline;)* -(A)>
Note that the A element type is part of the DTD parameter entity
"%inline;", but is excluded explicitly because of -(A).
Similarly, the following element type declaration for FORM prohibits
nested forms:
<!ELEMENT FORM - - (%block;|SCRIPT)+ -(FORM)>
3.3.4 Attribute declarations
The <!ATTLIST keyword begins the declaration of attributes that an
element may take. It is followed by the name of the element in
question, a list of attribute definitions, and a closing >. Each
attribute definition is a triplet that defines:
* The name of an attribute.
* The type of the attribute's value or an explicit set of possible
values. Values defined explicitly by the DTD are case-insensitive.
Please consult the section on basic HTML data types for more
information about attribute value types.
* Whether the default value of the attribute is implicit (keyword
"#IMPLIED"), in which case the default value must be supplied by
the user agent (in some cases via inheritance from parent
elements); always required (keyword "#REQUIRED"); or fixed to the
given value (keyword "#FIXED"). Some attribute definitions
explicitly specify a default value for the attribute.
In this example, the name attribute is defined for the MAP element.
The attribute is optional for this element.
<!ATTLIST MAP
name CDATA #IMPLIED
>
The type of values permitted for the attribute is given as CDATA, an
SGML data type. CDATA is text that may contain character references.
For more information about "CDATA", "NAME", "ID", and other data
types, please consult the section on HTML data types.
The following examples illustrate several attribute definitions:
rowspan NUMBER 1 -- number of rows spanned by cell --
http-equiv NAME #IMPLIED -- HTTP response header name --
id ID #IMPLIED -- document-wide unique id --
valign (top|middle|bottom|baseline) #IMPLIED
The rowspan attribute requires values of type NUMBER. The default
value is given explicitly as "1". The optional http-equiv attribute
requires values of type NAME. The optional id attribute requires
values of type ID. The optional valign attribute is constrained to
take values from the set {top, middle, bottom, baseline}.
DTD entities in attribute definitions
Attribute definitions may also contain parameter entity references.
In this example, we see that the attribute definition list for the
LINK element begins with the "%attrs;" parameter entity.
<!ELEMENT LINK - O EMPTY -- a media-independent link -->
<!ATTLIST LINK
%attrs; -- %coreattrs, %i18n, %events --
charset %Charset; #IMPLIED -- char encoding of linked resource --
href %URI; #IMPLIED -- URI for linked resource --
hreflang %LanguageCode; #IMPLIED -- language code --
type %ContentType; #IMPLIED -- advisory content type --
rel %LinkTypes; #IMPLIED -- forward link types --
rev %LinkTypes; #IMPLIED -- reverse link types --
media %MediaDesc; #IMPLIED -- for rendering on these media --
>
Start tag: required, End tag: forbidden
The "%attrs;" parameter entity is defined as follows:
<!ENTITY % attrs "%coreattrs; %i18n; %events;">
The "%coreattrs;" parameter entity in the "%attrs;" definition expands
as follows:
<!ENTITY % coreattrs
"id ID #IMPLIED -- document-wide unique id --
class CDATA #IMPLIED -- space-separated list of classes --
style %StyleSheet; #IMPLIED -- associated style info --
title %Text; #IMPLIED -- advisory title --"
>
The "%attrs;" parameter entity has been defined for convenience since
these attributes are defined for most HTML element types.
Similarly, the DTD defines the "%URI;" parameter entity as expanding
into the string "CDATA".
<!ENTITY % URI "CDATA"
-- a Uniform Resource Identifier,
see [URI]
-->
As this example illustrates, the parameter entity "%URI;" provides
readers of the DTD with more information as to the type of data
expected for an attribute. Similar entities have been defined for
"%Color;", "%Charset;", "%Length;", "%Pixels;", etc.
Boolean attributes
Some attributes play the role of boolean variables (e.g., the selected
attribute for the OPTION element). Their appearance in the start tag
of an element implies that the value of the attribute is "true". Their
absence implies a value of "false".
Boolean attributes may legally take a single value: the name of the
attribute itself (e.g., selected="selected").
This example defines the selected attribute to be a boolean attribute.
selected (selected) #IMPLIED -- option is pre-selected --
The attribute is set to "true" by appearing in the element's start
tag:
<OPTION selected="selected">
...contents...
</OPTION>
In HTML, boolean attributes may appear in minimized form -- the
attribute's value appears alone in the element's start tag. Thus,
selected may be set by writing:
<OPTION selected>
instead of:
<OPTION selected="selected">
Authors should be aware that many user agents only recognize the
minimized form of boolean attributes and not the full form.
4 Conformance: requirements and recommendations
Contents
1. Definitions
2. SGML
3. The text/html content type
In this section, we begin the specification of HTML 4, starting with
the contract between authors, documents, users, and user agents.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. However, for
readability, these words do not appear in all uppercase letters in
this specification.
At times, the authors of this specification recommend good practice
for authors and user agents. These recommendations are not normative
and conformance with this specification does not depend on their
realization. These recommendations contain the expression "We
recommend ...", "This specification recommends ...", or some similar
wording.
4.1 Definitions
HTML document
An HTML document is an SGML document that meets the constraints
of this specification.
Author
An author is a person or program that writes or generates HTML
documents. An authoring tool is a special case of an author,
namely, it's a program that generates HTML.
We recommend that authors write documents that conform to the
strict DTD rather than the other DTDs defined by this
specification. Please see the section on version information
for details about the DTDs defined in HTML 4.
User
A user is a person who interacts with a user agent to view,
hear, or otherwise use a rendered HTML document.
HTML user agent
An HTML user agent is any device that interprets HTML
documents. User agents include visual browsers (text-only and
graphical), non-visual browsers (audio, Braille), search
robots, proxies, etc.
A conforming user agent for HTML 4 is one that observes the
mandatory conditions ("must") set forth in this specification,
including the following points:
+ A user agent should avoid imposing arbitrary length limits on
attribute value literals (see the section on capacities in
the SGML Declaration). For introductory information on SGML
attributes, please consult the section on attribute
definitions.
+ A user agent must ensure that rendering is unchanged by the
presence or absence of start tags and end tags when the HTML
DTD indicates that these are optional. See the section on
element definitions for introductory information on SGML
elements.
+ For reasons of backwards compatibility, we recommend that
tools interpreting HTML 4 continue to support HTML 3.2 (see
[HTML32]) and HTML 2.0 (see [RFC1866]).
Error conditions
This specification does not define how conforming user agents
handle general error conditions, including how user agents
behave when they encounter elements, attributes, attribute
values, or entities not specified in this document.
However, for recommended error handling behavior, please
consult the notes on invalid documents.
Deprecated
A deprecated element or attribute is one that has been outdated
by newer constructs. Deprecated elements are defined in the
reference manual in appropriate locations, but are clearly
marked as deprecated. Deprecated elements may become obsolete
in future versions of HTML.
User agents should continue to support deprecated elements for
reasons of backward compatibility.
Definitions of elements and attributes clearly indicate which
are deprecated.
This specification includes examples that illustrate how to
avoid using deprecated elements. In most cases these depend on
user agent support for style sheets. In general, authors should
use style sheets to achieve stylistic and formatting effects
rather than HTML presentational attributes. HTML presentational
attributes have been deprecated when style sheet alternatives
exist (see, for example, [CSS1]).
Obsolete
An obsolete element or attribute is one for which there is no
guarantee of support by a user agent. Obsolete elements are no
longer defined in the specification, but are listed for
historical purposes in the changes section of the reference
manual.
4.2 SGML
HTML 4 is an SGML application conforming to International Standard ISO
8879 -- Standard Generalized Markup Language SGML (defined in
[ISO8879]).
Examples in the text conform to the strict document type definition
unless the example in question refers to elements or attributes only
defined by the transitional document type definition or frameset
document type definition. For the sake of brevity, most of the
examples in this specification do not begin with the document type
declaration that is mandatory at the beginning of each HTML document.
DTD fragments in element definitions come from the strict document
type definition except for the elements related to frames.
Please consult the section on HTML version information for details
about when to use the strict, transitional, or frameset DTD.
Comments appearing in the HTML 4 DTD have no normative value; they are
informative only.
User agents must not render SGML processing instructions (e.g., <?full
volume>) or comments. For more information about this and other SGML
features that may be legal in HTML but aren't widely supported by HTML
user agents, please consult the section on SGML features with limited
support.
4.3 The text/html content type
HTML documents are sent over the Internet as a sequence of bytes
accompanied by encoding information (described in the section on
character encodings). The structure of the transmission, termed a
message entity, is defined by [RFC2045] and [RFC2616]. A message
entity with a content type of "text/html" represents an HTML document.
The content type for HTML documents is defined as follows:
Content type name:
text
Content subtype name:
html
Required parameters:
none
Optional parameters:
charset
Encoding considerations:
any encoding is allowed
Security considerations:
See the notes on security
The optional parameter "charset" refers to the character encoding used
to represent the HTML document as a sequence of bytes. Legal values
for this parameter are defined in the section on character encodings.
Although this parameter is optional, we recommend that it always be
present.
5 HTML Document Representation
Contents
1. The Document Character Set
2. Character encodings
1. Choosing an encoding
o Notes on specific encodings
2. Specifying the character encoding
3. Character references
1. Numeric character references
2. Character entity references
4. Undisplayable characters
In this chapter, we discuss how HTML documents are represented on a
computer and over the Internet.
The section on the document character set addresses the issue of what
abstract characters may be part of an HTML document. Characters
include the Latin letter "A", the Cyrillic letter "I", the Chinese
character meaning "water", etc.
The section on character encodings addresses the issue of how those
characters may be represented in a file or when transferred over the
Internet. As some character encodings cannot directly represent all
characters an author may want to include in a document, HTML offers
other mechanisms, called character references, for referring to any
character.
Since there are a great number of characters throughout human
languages, and a great variety of ways to represent those characters,
proper care must be taken so that documents may be understood by user
agents around the world.
5.1 The Document Character Set
To promote interoperability, SGML requires that each application
(including HTML) specify its document character set. A document
character set consists of:
* A Repertoire: A set of abstract characters,, such as the Latin
letter "A", the Cyrillic letter "I", the Chinese character meaning
"water", etc.
* Code positions: A set of integer references to characters in the
repertoire.
Each SGML document (including each HTML document) is a sequence of
characters from the repertoire. Computer systems identify each
character by its code position; for example, in the ASCII character
set, code positions 65, 66, and 67 refer to the characters 'A', 'B',
and 'C', respectively.
The ASCII character set is not sufficient for a global information
system such as the Web, so HTML uses the much more complete character
set called the Universal Character Set (UCS), defined in [ISO10646].
This standard defines a repertoire of thousands of characters used by
communities all over the world.
The character set defined in [ISO10646] is character-by-character
equivalent to Unicode ([UNICODE]). Both of these standards are updated
from time to time with new characters, and the amendments should be
consulted at the respective Web sites. In the current specification,
"[ISO10646]" is used to refer to the document character set while
"[UNICODE]" is reserved for references to the Unicode bidirectional
text algorithm.
The document character set, however, does not suffice to allow user
agents to correctly interpret HTML documents as they are typically
exchanged -- encoded as a sequence of bytes in a file or during a
network transmission. User agents must also know the specific
character encoding that was used to transform the document character
stream into a byte stream.
5.2 Character encodings
What this specification calls a character encoding is known by
different names in other specifications (which may cause some
confusion). However, the concept is largely the same across the
Internet. Also, protocol headers, attributes, and parameters referring
to character encodings share the same name -- "charset" -- and use the
same values from the [IANA] registry (see [CHARSETS] for a complete
list).
The "charset" parameter identifies a character encoding, which is a
method of converting a sequence of bytes into a sequence of
characters. This conversion fits naturally with the scheme of Web
activity: servers send HTML documents to user agents as a stream of
bytes; user agents interpret them as a sequence of characters. The
conversion method can range from simple one-to-one correspondence to
complex switching schemes or algorithms.
A simple one-byte-per-character encoding technique is not sufficient
for text strings over a character repertoire as large as [ISO10646].
There are several different encodings of parts of [ISO10646] in
addition to encodings of the entire character set (such as UCS-4).
5.2.1 Choosing an encoding
Authoring tools (e.g., text editors) may encode HTML documents in the
character encoding of their choice, and the choice largely depends on
the conventions used by the system software. These tools may employ
any convenient encoding that covers most of the characters contained
in the document, provided the encoding is correctly labeled.
Occasional characters that fall outside this encoding may still be
represented by character references. These always refer to the
document character set, not the character encoding.
Servers and proxies may change a character encoding (called
transcoding) on the fly to meet the requests of user agents (see
section 14.2 of [RFC2616], the "Accept-Charset" HTTP request header).
Servers and proxies do not have to serve a document in a character
encoding that covers the entire document character set.
Commonly used character encodings on the Web include ISO-8859-1 (also
referred to as "Latin-1"; usable for most Western European languages),
ISO-8859-5 (which supports Cyrillic), SHIFT_JIS (a Japanese encoding),
EUC-JP (another Japanese encoding), and UTF-8 (an encoding of ISO
10646 using a different number of bytes for different characters).
Names for character encodings are case-insensitive, so that for
example "SHIFT_JIS", "Shift_JIS", and "shift_jis" are equivalent.
This specification does not mandate which character encodings a user
agent must support.
Conforming user agents must correctly map to ISO 10646 all characters
in any character encodings that they recognize (or they must behave as
if they did).
Notes on specific encodings
When HTML text is transmitted in UTF-16 (charset=UTF-16), text data
should be transmitted in network byte order ("big-endian", high-order
byte first) in accordance with [ISO10646], Section 6.3 and [UNICODE],
clause C3, page 3-1.
Furthermore, to maximize chances of proper interpretation, it is
recommended that documents transmitted as UTF-16 always begin with a
ZERO-WIDTH NON-BREAKING SPACE character (hexadecimal FEFF, also called
Byte Order Mark (BOM)) which, when byte-reversed, becomes hexadecimal
FFFE, a character guaranteed never to be assigned. Thus, a user-agent
receiving a hexadecimal FFFE as the first bytes of a text would know
that bytes have to be reversed for the remainder of the text.
The UTF-1 transformation format of [ISO10646] (registered by IANA as
ISO-10646-UTF-1), should not be used. For information about ISO 8859-8
and the bidirectional algorithm, please consult the section on
bidirectionality and character encoding.
5.2.2 Specifying the character encoding
How does a server determine which character encoding applies for a
document it serves? Some servers examine the first few bytes of the
document, or check against a database of known files and encodings.
Many modern servers give Web masters more control over charset
configuration than old servers do. Web masters should use these
mechanisms to send out a "charset" parameter whenever possible, but
should take care not to identify a document with the wrong "charset"
parameter value.
How does a user agent know which character encoding has been used? The
server should provide this information. The most straightforward way
for a server to inform the user agent about the character encoding of
the document is to use the "charset" parameter of the "Content-Type"
header field of the HTTP protocol ([RFC2616], sections 3.4 and 14.17)
For example, the following HTTP header announces that the character
encoding is EUC-JP:
Content-Type: text/html; charset=EUC-JP
Please consult the section on conformance for the definition of
text/html.
The HTTP protocol ([RFC2616], section 3.7.1) mentions ISO-8859-1 as a
default character encoding when the "charset" parameter is absent from
the "Content-Type" header field. In practice, this recommendation has
proved useless because some servers don't allow a "charset" parameter
to be sent, and others may not be configured to send the parameter.
Therefore, user agents must not assume any default value for the
"charset" parameter.
To address server or configuration limitations, HTML documents may
include explicit information about the document's character encoding;
the META element can be used to provide user agents with this
information.
For example, to specify that the character encoding of the current
document is "EUC-JP", a document should include the following META
declaration:
<META http-equiv="Content-Type" content="text/html; charset=EUC-JP">
The META declaration must only be used when the character encoding is
organized such that ASCII-valued bytes stand for ASCII characters (at
least until the META element is parsed). META declarations should
appear as early as possible in the HEAD element.
For cases where neither the HTTP protocol nor the META element
provides information about the character encoding of a document, HTML
also provides the charset attribute on several elements. By combining
these mechanisms, an author can greatly improve the chances that, when
the user retrieves a resource, the user agent will recognize the
character encoding.
To sum up, conforming user agents must observe the following
priorities when determining a document's character encoding (from
highest priority to lowest):
1. An HTTP "charset" parameter in a "Content-Type" field.
2. A META declaration with "http-equiv" set to "Content-Type" and a
value set for "charset".
3. The charset attribute set on an element that designates an
external resource.
In addition to this list of priorities, the user agent may use
heuristics and user settings. For example, many user agents use a
heuristic to distinguish the various encodings used for Japanese text.
Also, user agents typically have a user-definable, local default
character encoding which they apply in the absence of other
indicators.
User agents may provide a mechanism that allows users to override
incorrect "charset" information. However, if a user agent offers such
a mechanism, it should only offer it for browsing and not for editing,
to avoid the creation of Web pages marked with an incorrect "charset"
parameter.
Note. If, for a specific application, it becomes necessary to refer to
characters outside [ISO10646], characters should be assigned to a
private zone to avoid conflicts with present or future versions of the
standard. This is highly discouraged, however, for reasons of
portability.
5.3 Character references
A given character encoding may not be able to express all characters
of the document character set. For such encodings, or when hardware or
software configurations do not allow users to input some document
characters directly, authors may use SGML character references.
Character references are a character encoding-independent mechanism
for entering any character from the document character set.
Character references in HTML may appear in two forms:
* Numeric character references (either decimal or hexadecimal).
* Character entity references.
Character references within comments have no special meaning; they are
comment data only.
Note. HTML provides other ways to present character data, in
particular inline images.
Note. In SGML, it is possible to eliminate the final ";" after a
character reference in some cases (e.g., at a line break or
immediately before a tag). In other circumstances it may not be
eliminated (e.g., in the middle of a word). We strongly suggest using
the ";" in all cases to avoid problems with user agents that require
this character to be present.
5.3.1 Numeric character references
Numeric character references specify the code position of a character
in the document character set. Numeric character references may take
two forms:
* The syntax "&#D;", where D is a decimal number, refers to the ISO
10646 decimal character number D.
* The syntax "&#xH;" or "&#XH;", where H is a hexadecimal number,
refers to the ISO 10646 hexadecimal character number H.
Hexadecimal numbers in numeric character references are
case-insensitive.
Here are some examples of numeric character references:
* å (in decimal) represents the letter "a" with a small circle
above it (used, for example, in Norwegian).
* å (in hexadecimal) represents the same character.
* å (in hexadecimal) represents the same character as well.
* И (in decimal) represents the Cyrillic capital letter "I".
* 水 (in hexadecimal) represents the Chinese character for
water.
Note. Although the hexadecimal representation is not defined in
[ISO8879], it is expected to be in the revision, as described in
[WEBSGML]. This convention is particularly useful since character
standards generally use hexadecimal representations.
5.3.2 Character entity references
In order to give authors a more intuitive way of referring to
characters in the document character set, HTML offers a set of
character entity references. Character entity references use symbolic
names so that authors need not remember code positions. For example,
the character entity reference å refers to the lowercase "a"
character topped with a ring; "å" is easier to remember than
å.
HTML 4 does not define a character entity reference for every
character in the document character set. For instance, there is no
character entity reference for the Cyrillic capital letter "I". Please
consult the full list of character references defined in HTML 4.
Character entity references are case-sensitive. Thus, Å refers
to a different character (uppercase A, ring) than å (lowercase
a, ring).
Four character entity references deserve special mention since they
are frequently used to escape special characters:
* "<" represents the < sign.
* ">" represents the > sign.
* "&" represents the & sign.
* "" represents the " mark.
Authors wishing to put the "<" character in text should use "<"
(ASCII decimal 60) to avoid possible confusion with the beginning of a
tag (start tag open delimiter). Similarly, authors should use ">"
(ASCII decimal 62) in text instead of ">" to avoid problems with older
user agents that incorrectly perceive this as the end of a tag (tag
close delimiter) when it appears in quoted attribute values.
Authors should use "&" (ASCII decimal 38) instead of "&" to avoid
confusion with the beginning of a character reference (entity
reference open delimiter). Authors should also use "&" in
attribute values since character references are allowed within CDATA
attribute values.
Some authors use the character entity reference """ to encode
instances of the double quote mark (") since that character may be
used to delimit attribute values.
5.4 Undisplayable characters
A user agent may not be able to render all characters in a document
meaningfully, for instance, because the user agent lacks a suitable
font, a character has a value that may not be expressed in the user
agent's internal character encoding, etc.
Because there are many different things that may be done in such
cases, this document does not prescribe any specific behavior.
Depending on the implementation, undisplayable characters may also be
handled by the underlying display system and not the application
itself. In the absence of more sophisticated behavior, for example
tailored to the needs of a particular script or language, we recommend
the following behavior for user agents:
1. Adopt a clearly visible, but unobtrusive mechanism to alert the
user of missing resources.
2. If missing characters are presented using their numeric
representation, use the hexadecimal (not decimal) form since this
is the form used in character set standards.
6 Basic HTML data types
Contents
1. Case information
2. SGML basic types
3. Text strings
4. URIs
5. Colors
1. Notes on using colors
6. Lengths
7. Content types (MIME types)
8. Language codes
9. Character encodings
10. Single characters
11. Dates and times
12. Link types
13. Media descriptors
14. Script data
15. Style sheet data
16. Frame target names
This section of the specification describes the basic data types that
may appear as an element's content or an attribute's value.
For introductory information about reading the HTML DTD, please
consult the SGML tutorial.
6.1 Case information
Each attribute definition includes information about the
case-sensitivity of its values. The case information is presented with
the following keys:
CS
The value is case-sensitive (i.e., user agents interpret "a"
and "A" differently).
CI
The value is case-insensitive (i.e., user agents interpret "a"
and "A" as the same).
CN
The value is not subject to case changes, e.g., because it is a
number or a character from the document character set.
CA
The element or attribute definition itself gives case
information.
CT
Consult the type definition for details about case-sensitivity.
If an attribute value is a list, the keys apply to every value in the
list, unless otherwise indicated.
6.2 SGML basic types
The document type definition specifies the syntax of HTML element
content and attribute values using SGML tokens (e.g., PCDATA, CDATA,
NAME, ID, etc.). See [ISO8879] for their full definitions. The
following is a summary of key information:
* CDATA is a sequence of characters from the document character set
and may include character entities. User agents should interpret
attribute values as follows:
+ Replace character entities with characters,
+ Ignore line feeds,
+ Replace each carriage return or tab with a single space.
User agents may ignore leading and trailing white space in CDATA
attribute values (e.g., " myval " may be interpreted as
"myval"). Authors should not declare attribute values with leading
or trailing white space.
For some HTML 4 attributes with CDATA attribute values, the
specification imposes further constraints on the set of legal
values for the attribute that may not be expressed by the DTD.
Although the STYLE and SCRIPT elements use CDATA for their data
model, for these elements, CDATA must be handled differently by
user agents. Markup and entities must be treated as raw text and
passed to the application as is. The first occurrence of the
character sequence "</" (end-tag open delimiter) is treated as
terminating the end of the element's content. In valid documents,
this would be the end tag for the element.
* ID and NAME tokens must begin with a letter ([A-Za-z]) and may be
followed by any number of letters, digits ([0-9]), hyphens ("-"),
underscores ("_"), colons (":"), and periods (".").
* IDREF and IDREFS are references to ID tokens defined by other
attributes. IDREF is a single token and IDREFS is a
space-separated list of tokens.
* NUMBER tokens must contain at least one digit ([0-9]).
6.3 Text strings
A number of attributes ( %Text; in the DTD) take text that is meant to
be "human readable". For introductory information about attributes,
please consult the tutorial discussion of attributes.
6.4 URIs
This specification uses the term URI as defined in [URI] (see also
[RFC1630]).
Note that URIs include URLs (as defined in [RFC1738] and [RFC1808]).
Relative URIs are resolved to full URIs using a base URI. [RFC1808],
section 3, defines the normative algorithm for this process. For more
information about base URIs, please consult the section on base URIs
in the chapter on links.
URIs are represented in the DTD by the parameter entity %URI;.
URIs in general are case-sensitive. There may be URIs, or parts of
URIs, where case doesn't matter (e.g., machine names), but identifying
these may not be easy. Users should always consider that URIs are
case-sensitive (to be on the safe side).
Please consult the appendix for information about non-ASCII characters
in URI attribute values.
6.5 Colors
The attribute value type "color" (%Color;) refers to color definitions
as specified in [SRGB]. A color value may either be a hexadecimal
number (prefixed by a hash mark) or one of the following sixteen color
names. The color names are case-insensitive.
CAPTION: Color names and sRGB values
Black = "#000000" Green = "#008000"
Silver = "#C0C0C0" Lime = "#00FF00"
Gray = "#808080" Olive = "#808000"
White = "#FFFFFF" Yellow = "#FFFF00"
Maroon = "#800000" Navy = "#000080"
Red = "#FF0000" Blue = "#0000FF"
Purple = "#800080" Teal = "#008080"
Fuchsia = "#FF00FF" Aqua = "#00FFFF"
Thus, the color values "#800080" and "Purple" both refer to the color
purple.
6.5.1 Notes on using colors
Although colors can add significant amounts of information to
documents and make them more readable, please consider the following
guidelines when including color in your documents:
* The use of HTML elements and attributes for specifying color is
deprecated. You are encouraged to use style sheets instead.
* Don't use color combinations that cause problems for people with
color blindness in its various forms.
* If you use a background image or set the background color, then be
sure to set the various text colors as well.
* Colors specified with the BODY and FONT elements and bgcolor on
tables look different on different platforms (e.g., workstations,
Macs, Windows, and LCD panels vs. CRTs), so you shouldn't rely
entirely on a specific effect. In the future, support for the
[SRGB] color model together with ICC color profiles should
mitigate this problem.
* When practical, adopt common conventions to minimize user
confusion.
6.6 Lengths
HTML specifies three types of length values for attributes:
1. Pixels: The value (%Pixels; in the DTD) is an integer that
represents the number of pixels of the canvas (screen, paper).
Thus, the value "50" means fifty pixels. For normative information
about the definition of a pixel, please consult [CSS1].
2. Length: The value (%Length; in the DTD) may be either a %Pixel; or
a percentage of the available horizontal or vertical space. Thus,
the value "50%" means half of the available space.
3. MultiLength: The value ( %MultiLength; in the DTD) may be a
%Length; or a relative length. A relative length has the form
"i*", where "i" is an integer. When allotting space among elements
competing for that space, user agents allot pixel and percentage
lengths first, then divide up remaining available space among
relative lengths. Each relative length receives a portion of the
available space that is proportional to the integer preceding the
"*". The value "*" is equivalent to "1*". Thus, if 60 pixels of
space are available after the user agent allots pixel and
percentage space, and the competing relative lengths are 1*, 2*,
and 3*, the 1* will be alloted 10 pixels, the 2* will be alloted
20 pixels, and the 3* will be alloted 30 pixels.
Length values are case-neutral.
6.7 Content types (MIME types)
Note. A "media type" (defined in [RFC2045] and [RFC2046]) specifies
the nature of a linked resource. This specification employs the term
"content type" rather than "media type" in accordance with current
usage. Furthermore, in this specification, "media type" may refer to
the media where a user agent renders a document.
This type is represented in the DTD by %ContentType;.
Content types are case-insensitive.
Examples of content types include "text/html", "image/png",
"image/gif", "video/mpeg", "text/css", and "audio/basic". For the
current list of registered MIME types, please consult [MIMETYPES].
6.8 Language codes
The value of attributes whose type is a language code ( %LanguageCode
in the DTD) refers to a language code as specified by [RFC1766],
section 2. For information on specifying language codes in HTML,
please consult the section on language codes. Whitespace is not
allowed within the language-code.
Language codes are case-insensitive.
6.9 Character encodings
The "charset" attributes (%Charset in the DTD) refer to a character
encoding as described in the section on character encodings. Values
must be strings (e.g., "euc-jp") from the IANA registry (see
[CHARSETS] for a complete list).
Names of character encodings are case-insensitive.
User agents must follow the steps set out in the section on specifying
character encodings in order to determine the character encoding of an
external resource.
6.10 Single characters
Certain attributes call for a single character from the document
character set. These attributes take the %Character type in the DTD.
Single characters may be specified with character references (e.g.,
"&").
6.11 Dates and times
[ISO8601] allows many options and variations in the representation of
dates and times. The current specification uses one of the formats
described in the profile [DATETIME] for its definition of legal
date/time strings ( %Datetime in the DTD).
The format is:
YYYY-MM-DDThh:mm:ssTZD
where:
YYYY = four-digit year
MM = two-digit month (01=January, etc.)
DD = two-digit day of month (01 through 31)
hh = two digits of hour (00 through 23) (am/pm NOT allowed)
mm = two digits of minute (00 through 59)
ss = two digits of second (00 through 59)
TZD = time zone designator
The time zone designator is one of:
Z
indicates UTC (Coordinated Universal Time). The "Z" must be
uppercase.
+hh:mm
indicates that the time is a local time which is hh hours and
mm minutes ahead of UTC.
-hh:mm
indicates that the time is a local time which is hh hours and
mm minutes behind UTC.
Exactly the components shown here must be present, with exactly this
punctuation. Note that the "T" appears literally in the string (it
must be uppercase), to indicate the beginning of the time element, as
specified in [ISO8601]
If a generating application does not know the time to the second, it
may use the value "00" for the seconds (and minutes and hours if
necessary).
Note. [DATETIME] does not address the issue of leap seconds.
6.12 Link types
Authors may use the following recognized link types, listed here with
their conventional interpretations. In the DTD, %LinkTypes refers to a
space-separated list of link types. White space characters are not
permitted within link types.
These link types are case-insensitive, i.e., "Alternate" has the same
meaning as "alternate".
User agents, search engines, etc. may interpret these link types in a
variety of ways. For example, user agents may provide access to linked
documents through a navigation bar.
Alternate
Designates substitute versions for the document in which the
link occurs. When used together with the lang attribute, it
implies a translated version of the document. When used
together with the media attribute, it implies a version
designed for a different medium (or media).
Stylesheet
Refers to an external style sheet. See the section on external
style sheets for details. This is used together with the link
type "Alternate" for user-selectable alternate style sheets.
Start
Refers to the first document in a collection of documents. This
link type tells search engines which document is considered by
the author to be the starting point of the collection.
Next
Refers to the next document in a linear sequence of documents.
User agents may choose to preload the "next" document, to
reduce the perceived load time.
Prev
Refers to the previous document in an ordered series of
documents. Some user agents also support the synonym
"Previous".
Contents
Refers to a document serving as a table of contents. Some user
agents also support the synonym ToC (from "Table of Contents").
Index
Refers to a document providing an index for the current
document.
Glossary
Refers to a document providing a glossary of terms that pertain
to the current document.
Copyright
Refers to a copyright statement for the current document.
Chapter
Refers to a document serving as a chapter in a collection of
documents.
Section
Refers to a document serving as a section in a collection of
documents.
Subsection
Refers to a document serving as a subsection in a collection of
documents.
Appendix
Refers to a document serving as an appendix in a collection of
documents.
Help
Refers to a document offering help (more information, links to
other sources information, etc.)
Bookmark
Refers to a bookmark. A bookmark is a link to a key entry point
within an extended document. The title attribute may be used,
for example, to label the bookmark. Note that several bookmarks
may be defined in each document.
Authors may wish to define additional link types not described in this
specification. If they do so, they should use a profile to cite the
conventions used to define the link types. Please see the profile
attribute of the HEAD element for more details.
For further discussions about link types, please consult the section
on links in HTML documents.
6.13 Media descriptors
The following is a list of recognized media descriptors ( %MediaDesc
in the DTD).
screen
Intended for non-paged computer screens.
tty
Intended for media using a fixed-pitch character grid, such as
teletypes, terminals, or portable devices with limited display
capabilities.
tv
Intended for television-type devices (low resolution, color,
limited scrollability).
projection
Intended for projectors.
handheld
Intended for handheld devices (small screen, monochrome,
bitmapped graphics, limited bandwidth).
print
Intended for paged, opaque material and for documents viewed on
screen in print preview mode.
braille
Intended for braille tactile feedback devices.
aural
Intended for speech synthesizers.
all
Suitable for all devices.
Future versions of HTML may introduce new values and may allow
parameterized values. To facilitate the introduction of these
extensions, conforming user agents must be able to parse the media
attribute value as follows:
1. The value is a comma-separated list of entries. For example,
media="screen, 3d-glasses, print and resolution > 90dpi"
is mapped to:
"screen"
"3d-glasses"
"print and resolution > 90dpi"
2. Each entry is truncated just before the first character that isn't
a US ASCII letter [a-zA-Z] (ISO 10646 hex 41-5a, 61-7a), digit
[0-9] (hex 30-39), or hyphen (hex 2d). In the example, this gives:
"screen"
"3d-glasses"
"print"
3. A case-sensitive match is then made with the set of media types
defined above. User agents may ignore entries that don't match. In
the example we are left with screen and print.
Note. Style sheets may include media-dependent variations within them
(e.g., the CSS @media construct). In such cases it may be appropriate
to use "media=all".
6.14 Script data
Script data ( %Script; in the DTD) can be the content of the SCRIPT
element and the value of intrinsic event attributes. User agents must
not evaluate script data as HTML markup but instead must pass it on as
data to a script engine.
The case-sensitivity of script data depends on the scripting language.
Please note that script data that is element content may not contain
character references, but script data that is the value of an
attribute may contain them. The appendix provides further information
about specifying non-HTML data.
6.15 Style sheet data
Style sheet data (%StyleSheet; in the DTD) can be the content of the
STYLE element and the value of the style attribute. User agents must
not evaluate style data as HTML markup.
The case-sensitivity of style data depends on the style sheet
language.
Please note that style sheet data that is element content may not
contain character references, but style sheet data that is the value
of an attribute may contain them. The appendix provides further
information about specifying non-HTML data.
6.16 Frame target names
Except for the reserved names listed below, frame target names
(%FrameTarget; in the DTD) must begin with an alphabetic character
(a-zA-Z). User agents should ignore all other target names.
The following target names are reserved and have special meanings.
_blank
The user agent should load the designated document in a new,
unnamed window.
_self
The user agent should load the document in the same frame as
the element that refers to this target.
_parent
The user agent should load the document into the immediate
FRAMESET parent of the current frame. This value is equivalent
to _self if the current frame has no parent.
_top
The user agent should load the document into the full, original
window (thus canceling all other frames). This value is
equivalent to _self if the current frame has no parent.
7 The global structure of an HTML document
Contents
1. Introduction to the structure of an HTML document
2. HTML version information
3. The HTML element
4. The document head
1. The HEAD element
2. The TITLE element
3. The title attribute
4. Meta data
o Specifying meta data
o The META element
o Meta data profiles
5. The document body
1. The BODY element
2. Element identifiers: the id and class attributes
3. Block-level and inline elements
4. Grouping elements: the DIV and SPAN elements
5. Headings: The H1, H2, H3, H4, H5, H6 elements
6. The ADDRESS element
7.1 Introduction to the structure of an HTML document
An HTML 4 document is composed of three parts:
1. a line containing HTML version information,
2. a declarative header section (delimited by the HEAD element),
3. a body, which contains the document's actual content. The body may
be implemented by the BODY element or the FRAMESET element.
White space (spaces, newlines, tabs, and comments) may appear before
or after each section. Sections 2 and 3 should be delimited by the
HTML element.
Here's an example of a simple HTML document:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>My first HTML document</TITLE>
</HEAD>
<BODY>
<P>Hello world!
</BODY>
</HTML>
7.2 HTML version information
A valid HTML document declares what version of HTML is used in the
document. The document type declaration names the document type
definition (DTD) in use for the document (see [ISO8879]).
HTML 4.01 specifies three DTDs, so authors must include one of the
following document type declarations in their documents. The DTDs vary
in the elements they support.
* The HTML 4.01 Strict DTD includes all elements and attributes that
have not been deprecated or do not appear in frameset documents.
For documents that use this DTD, use this document type
declaration:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
* The HTML 4.01 Transitional DTD includes everything in the strict
DTD plus deprecated elements and attributes (most of which concern
visual presentation). For documents that use this DTD, use this
document type declaration:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
* The HTML 4.01 Frameset DTD includes everything in the transitional
DTD plus frames as well. For documents that use this DTD, use this
document type declaration:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
The URI in each document type declaration allows user agents to
download the DTD and any entity sets that are needed. The following
(relative) URIs refer to DTDs and entity sets for HTML 4:
* "strict.dtd" -- default strict DTD
* "loose.dtd" -- loose DTD
* "frameset.dtd" -- DTD for frameset documents
* "HTMLlat1.ent" -- Latin-1 entities
* "HTMLsymbol.ent" -- Symbol entities
* "HTMLspecial.ent" -- Special entities
The binding between public identifiers and files can be specified
using a catalog file following the format recommended by the Oasis
Open Consortium (see [OASISOPEN]). A sample catalog file for HTML 4.01
is included at the beginning of the section on SGML reference
information for HTML. The last two letters of the declaration indicate
the language of the DTD. For HTML, this is always English ("EN").
Note. As of the 24 December version of HTML 4.01, the HTML Working
Group commits to the following policy:
* Any changes to future HTML 4 DTDs will not invalidate documents
that conform to the DTDs of the present specification. The HTML
Working Group reserves the right to correct known bugs.
* Software conforming to the DTDs of the present specification may
ignore features of future HTML 4 DTDs that it does not recognize.
This means that in a document type declaration, authors may safely use
a system identifier that refers to the latest version of an HTML 4
DTD. Authors may also choose to use a system identifier that refers to
a specific (dated) version of an HTML 4 DTD when validation to that
particular DTD is required. W3C will make every effort to make
archival documents indefinitely available at their original address in
their original form.
7.3 The HTML element
<!ENTITY % html.content "HEAD, BODY">
<!ELEMENT HTML O O (%html.content;) -- document root element -->
<!ATTLIST HTML
%i18n; -- lang, dir --
>
Start tag: optional, End tag: optional
Attribute definitions
version = cdata [CN]
Deprecated. The value of this attribute specifies which HTML
DTD version governs the current document. This attribute has
been deprecated because it is redundant with version
information provided by the document type declaration.
Attributes defined elsewhere
* lang (language information), dir (text direction)
After document type declaration, the remainder of an HTML document is
contained by the HTML element. Thus, a typical HTML document has this
structure:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
...The head, body, etc. goes here...
</HTML>
7.4 The document head
7.4.1 The HEAD element
<!-- %head.misc; defined earlier on as "SCRIPT|STYLE|META|LINK|OBJECT" -->
<!ENTITY % head.content "TITLE & BASE?">
<!ELEMENT HEAD O O (%head.content;) +(%head.misc;) -- document head -->
<!ATTLIST HEAD
%i18n; -- lang, dir --
profile %URI; #IMPLIED -- named dictionary of meta info --
>
Start tag: optional, End tag: optional
Attribute definitions
profile = uri [CT]
This attribute specifies the location of one or more meta data
profiles, separated by white space. For future extensions, user
agents should consider the value to be a list even though this
specification only considers the first URI to be significant.
Profiles are discussed below in the section on meta data.
Attributes defined elsewhere
* lang (language information), dir (text direction)
The HEAD element contains information about the current document, such
as its title, keywords that may be useful to search engines, and other
data that is not considered document content. User agents do not
generally render elements that appear in the HEAD as content. They
may, however, make information in the HEAD available to users through
other mechanisms.
7.4.2 The TITLE element
<!-- The TITLE element is not considered part of the flow of text.
It should be displayed, for example as the page header or
window title. Exactly one title is required per document.
-->
<!ELEMENT TITLE - - (#PCDATA) -(%head.misc;) -- document title -->
<!ATTLIST TITLE %i18n>
Start tag: required, End tag: required
Attributes defined elsewhere
* lang (language information), dir (text direction)
Every HTML document must have a TITLE element in the HEAD section.
Authors should use the TITLE element to identify the contents of a
document. Since users often consult documents out of context, authors
should provide context-rich titles. Thus, instead of a title such as
"Introduction", which doesn't provide much contextual background,
authors should supply a title such as "Introduction to Medieval
Bee-Keeping" instead.
For reasons of accessibility, user agents must always make the content
of the TITLE element available to users (including TITLE elements that
occur in frames). The mechanism for doing so depends on the user agent
(e.g., as a caption, spoken).
Titles may contain character entities (for accented characters,
special characters, etc.), but may not contain other markup (including
comments). Here is a sample document title:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>A study of population dynamics</TITLE>
... other head elements...
</HEAD>
<BODY>
... document body...
</BODY>
</HTML>
7.4.3 The title attribute
Attribute definitions
title = text [CS]
This attribute offers advisory information about the element
for which it is set.
Unlike the TITLE element, which provides information about an entire
document and may only appear once, the title attribute may annotate
any number of elements. Please consult an element's definition to
verify that it supports this attribute.
Values of the title attribute may be rendered by user agents in a
variety of ways. For instance, visual browsers frequently display the
title as a "tool tip" (a short message that appears when the pointing
device pauses over an object). Audio user agents may speak the title
information in a similar context. For example, setting the attribute
on a link allows user agents (visual and non-visual) to tell users
about the nature of the linked resource:
...some text...
Here's a photo of
<A href="http://someplace.com/neatstuff.gif" title="Me scuba diving">
me scuba diving last summer
</A>
...some more text...
The title attribute has an additional role when used with the LINK
element to designate an external style sheet. Please consult the
section on links and style sheets for details.
Note. To improve the quality of speech synthesis for cases handled
poorly by standard techniques, future versions of HTML may include an
attribute for encoding phonemic and prosodic information.
7.4.4 Meta data
Note. The W3C Resource Description Framework (see [RDF10]) became a
W3C Recommendation in February 1999. RDF allows authors to specify
machine-readable metadata about HTML documents and other
network-accessible resources.
HTML lets authors specify meta data -- information about a document
rather than document content -- in a variety of ways.
For example, to specify the author of a document, one may use the META
element as follows:
<META name="Author" content="Dave Raggett">
The META element specifies a property (here "Author") and assigns a
value to it (here "Dave Raggett").
This specification does not define a set of legal meta data
properties. The meaning of a property and the set of legal values for
that property should be defined in a reference lexicon called a
profile. For example, a profile designed to help search engines index
documents might define properties such as "author", "copyright",
"keywords", etc.
Specifying meta data
In general, specifying meta data involves two steps:
1. Declaring a property and a value for that property. This may be
done in two ways:
1. From within a document, via the META element.
2. From outside a document, by linking to meta data via the LINK
element (see the section on link types).
2. Referring to a profile where the property and its legal values are
defined. To designate a profile, use the profile attribute of the
HEAD element.
Note that since a profile is defined for the HEAD element, the same
profile applies to all META and LINK elements in the document head.
User agents are not required to support meta data mechanisms. For
those that choose to support meta data, this specification does not
define how meta data should be interpreted.
The META element
<!ELEMENT META - O EMPTY -- generic metainformation -->
<!ATTLIST META
%i18n; -- lang, dir, for use with content --
http-equiv NAME #IMPLIED -- HTTP response header name --
name NAME #IMPLIED -- metainformation name --
content CDATA #REQUIRED -- associated information --
scheme CDATA #IMPLIED -- select form of content --
>
Start tag: required, End tag: forbidden
Attribute definitions
For the following attributes, the permitted values and their
interpretation are profile dependent:
name = name [CS]
This attribute identifies a property name. This specification
does not list legal values for this attribute.
content = cdata [CS]
This attribute specifies a property's value. This specification
does not list legal values for this attribute.
scheme = cdata [CS]
This attribute names a scheme to be used to interpret the
property's value (see the section on profiles for details).
http-equiv = name [CI]
This attribute may be used in place of the name attribute. HTTP
servers use this attribute to gather information for HTTP
response message headers.
Attributes defined elsewhere
* lang (language information), dir (text direction)
The META element can be used to identify properties of a document
(e.g., author, expiration date, a list of key words, etc.) and assign
values to those properties. This specification does not define a
normative set of properties.
Each META element specifies a property/value pair. The name attribute
identifies the property and the content attribute specifies the
property's value.
For example, the following declaration sets a value for the Author
property:
<META name="Author" content="Dave Raggett">
The lang attribute can be used with META to specify the language for
the value of the content attribute. This enables speech synthesizers
to apply language dependent pronunciation rules.
In this example, the author's name is declared to be French:
<META name="Author" lang="fr" content="Arnaud Le Hors">
Note. The META element is a generic mechanism for specifying meta
data. However, some HTML elements and attributes already handle
certain pieces of meta data and may be used by authors instead of META
to specify those pieces: the TITLE element, the ADDRESS element, the
INS and DEL elements, the title attribute, and the cite attribute.
Note. When a property specified by a META element takes a value that
is a URI, some authors prefer to specify the meta data via the LINK
element. Thus, the following meta data declaration:
<META name="DC.identifier"
content="http://www.ietf.org/rfc/rfc1866.txt">
might also be written:
<LINK rel="DC.identifier"
type="text/plain"
href="http://www.ietf.org/rfc/rfc1866.txt">
META and HTTP headers
The http-equiv attribute can be used in place of the name attribute
and has a special significance when documents are retrieved via the
Hypertext Transfer Protocol (HTTP). HTTP servers may use the property
name specified by the http-equiv attribute to create an [RFC822]-style
header in the HTTP response. Please see the HTTP specification
([RFC2616]) for details on valid HTTP headers.
The following sample META declaration:
<META http-equiv="Expires" content="Tue, 20 Aug 1996 14:25:27 GMT">
will result in the HTTP header:
Expires: Tue, 20 Aug 1996 14:25:27 GMT
This can be used by caches to determine when to fetch a fresh copy of
the associated document.
Note. Some user agents support the use of META to refresh the current
page after a specified number of seconds, with the option of replacing
it by a different URI. Authors should not use this technique to
forward users to different pages, as this makes the page inaccessible
to some users. Instead, automatic page forwarding should be done using
server-side redirects.
META and search engines
A common use for META is to specify keywords that a search engine may
use to improve the quality of search results. When several META
elements provide language-dependent information about a document,
search engines may filter on the lang attribute to display search
results using the language preferences of the user. For example,
<-- For speakers of US English -->
<META name="keywords" lang="en-us"
content="vacation, Greece, sunshine">
<-- For speakers of British English -->
<META name="keywords" lang="en"
content="holiday, Greece, sunshine">
<-- For speakers of French -->
<META name="keywords" lang="fr"
content="vacances, Grèce, soleil">
The effectiveness of search engines can also be increased by using the
LINK element to specify links to translations of the document in other
languages, links to versions of the document in other media (e.g.,
PDF), and, when the document is part of a collection, links to an
appropriate starting point for browsing the collection.
Further help is provided in the section on helping search engines
index your Web site.
META and PICS
The Platform for Internet Content Selection (PICS, specified in
[PICS]) is an infrastructure for associating labels (meta data) with
Internet content. Originally designed to help parents and teachers
control what children can access on the Internet, it also facilitates
other uses for labels, including code signing, privacy, and
intellectual property rights management.
This example illustrates how one can use a META declaration to include
a PICS 1.1 label:
<HEAD>
<META http-equiv="PICS-Label" content='
(PICS-1.1 "http://www.gcf.org/v2.5"
labels on "1994.11.05T08:15-0500"
until "1995.12.31T23:59-0000"
for "http://w3.org/PICS/Overview.html"
ratings (suds 0.5 density 0 color/hue 1))
'>
<TITLE>... document title ...</TITLE>
</HEAD>
META and default information
The META element may be used to specify the default information for a
document in the following instances:
* The default scripting language.
* The default style sheet language.
* The document character encoding.
The following example specifies the character encoding for a document
as being ISO-8859-5
<META http-equiv="Content-Type" content="text/html; charset=ISO-8859-5">
Meta data profiles
The profile attribute of the HEAD specifies the location of a meta
data profile. The value of the profile attribute is a URI. User agents
may use this URI in two ways:
* As a globally unique name. User agents may be able to recognize
the name (without actually retrieving the profile) and perform
some activity based on known conventions for that profile. For
instance, search engines could provide an interface for searching
through catalogs of HTML documents, where these documents all use
the same profile for representing catalog entries.
* As a link. User agents may dereference the URI and perform some
activity based on the actual definitions within the profile (e.g.,
authorize the usage of the profile within the current HTML
document). This specification does not define formats for
profiles.
This example refers to a hypothetical profile that defines useful
properties for document indexing. The properties defined by this
profile -- including "author", "copyright", "keywords", and "date" --
have their values set by subsequent META declarations.
<HEAD profile="http://www.acme.com/profiles/core">
<TITLE>How to complete Memorandum cover sheets</TITLE>
<META name="author" content="John Doe">
<META name="copyright" content="© 1997 Acme Corp.">
<META name="keywords" content="corporate,guidelines,cataloging">
<META name="date" content="1994-11-06T08:49:37+00:00">
</HEAD>
As this specification is being written, it is common practice to use
the date formats described in [RFC2616], section 3.3. As these formats
are relatively hard to process, we recommend that authors use the
[ISO8601] date format. For more information, see the sections on the
INS and DEL elements.
The scheme attribute allows authors to provide user agents more
context for the correct interpretation of meta data. At times, such
additional information may be critical, as when meta data may be
specified in different formats. For example, an author might specify a
date in the (ambiguous) format "10-9-97"; does this mean 9 October
1997 or 10 September 1997? The scheme attribute value "Month-Day-Year"
would disambiguate this date value.
At other times, the scheme attribute may provide helpful but
non-critical information to user agents.
For example, the following scheme declaration may help a user agent
determine that the value of the "identifier" property is an ISBN code
number:
<META scheme="ISBN" name="identifier" content="0-8230-2355-9">
Values for the scheme attribute depend on the property name and the
associated profile.
Note. One sample profile is the Dublin Core (see [DCORE]). This
profile defines a set of recommended properties for electronic
bibliographic descriptions, and is intended to promote
interoperability among disparate description models.
7.5 The document body
7.5.1 The BODY element
<!ELEMENT BODY O O (%block;|SCRIPT)+ +(INS|DEL) -- document body -->
<!ATTLIST BODY
%attrs; -- %coreattrs, %i18n, %events --
onload %Script; #IMPLIED -- the document has been loaded --
onunload %Script; #IMPLIED -- the document has been removed --
>
Start tag: optional, End tag: optional
Attribute definitions
background = uri [CT]
Deprecated. The value of this attribute is a URI that
designates an image resource. The image generally tiles the
background (for visual browsers).
text = color [CI]
Deprecated. This attribute sets the foreground color for text
(for visual browsers).
link = color [CI]
Deprecated. This attribute sets the color of text marking
unvisited hypertext links (for visual browsers).
vlink = color [CI]
Deprecated. This attribute sets the color of text marking
visited hypertext links (for visual browsers).
alink = color [CI]
Deprecated. This attribute sets the color of text marking
hypertext links when selected by the user (for visual
browsers).
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* bgcolor (background color)
* onload, onunload (intrinsic events)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
The body of a document contains the document's content. The content
may be presented by a user agent in a variety of ways. For example,
for visual browsers, you can think of the body as a canvas where the
content appears: text, images, colors, graphics, etc. For audio user
agents, the same content may be spoken. Since style sheets are now the
preferred way to specify a document's presentation, the presentational
attributes of BODY have been deprecated.
DEPRECATED EXAMPLE:
The following HTML fragment illustrates the use of the deprecated
attributes. It sets the background color of the canvas to white, the
text foreground color to black, and the color of hyperlinks to red
initially, fuchsia when activated, and maroon once visited.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<HTML>
<HEAD>
<TITLE>A study of population dynamics</TITLE>
</HEAD>
<BODY bgcolor="white" text="black"
link="red" alink="fuchsia" vlink="maroon">
... document body...
</BODY>
</HTML>
Using style sheets, the same effect could be accomplished as follows:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>A study of population dynamics</TITLE>
<STYLE type="text/css">
BODY { background: white; color: black}
A:link { color: red }
A:visited { color: maroon }
A:active { color: fuchsia }
</STYLE>
</HEAD>
<BODY>
... document body...
</BODY>
</HTML>
Using external (linked) style sheets gives you the flexibility to
change the presentation without revising the source HTML document:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>A study of population dynamics</TITLE>
<LINK rel="stylesheet" type="text/css" href="smartstyle.css">
</HEAD>
<BODY>
... document body...
</BODY>
</HTML>
Framesets and HTML bodies. Documents that contain framesets replace
the BODY element by the FRAMESET element. Please consult the section
on frames for more information.
7.5.2 Element identifiers: the id and class attributes
Attribute definitions
id = name [CS]
This attribute assigns a name to an element. This name must be
unique in a document.
class = cdata-list [CS]
This attribute assigns a class name or set of class names to an
element. Any number of elements may be assigned the same class
name or names. Multiple class names must be separated by white
space characters.
The id attribute assigns a unique identifier to an element (which may
be verified by an SGML parser). For example, the following paragraphs
are distinguished by their id values:
<P id="myparagraph"> This is a uniquely named paragraph.</P>
<P id="yourparagraph"> This is also a uniquely named paragraph.</P>
The id attribute has several roles in HTML:
* As a style sheet selector.
* As a target anchor for hypertext links.
* As a means to reference a particular element from a script.
* As the name of a declared OBJECT element.
* For general purpose processing by user agents (e.g. for
identifying fields when extracting data from HTML pages into a
database, translating HTML documents into other formats, etc.).
The class attribute, on the other hand, assigns one or more class
names to an element; the element may be said to belong to these
classes. A class name may be shared by several element instances. The
class attribute has several roles in HTML:
* As a style sheet selector (when an author wishes to assign style
information to a set of elements).
* For general purpose processing by user agents.
In the following example, the SPAN element is used in conjunction with
the id and class attributes to markup document messages. Messages
appear in both English and French versions.
<!-- English messages -->
<P><SPAN id="msg1" class="info" lang="en">Variable declared twice</SPAN>
<P><SPAN id="msg2" class="warning" lang="en">Undeclared variable</SPAN>
<P><SPAN id="msg3" class="error" lang="en">Bad syntax for variable name</SPAN>
<!-- French messages -->
<P><SPAN id="msg1" class="info" lang="fr">Variable déclarée deux
fois</SPAN>
<P><SPAN id="msg2" class="warning" lang="fr">Variable indéfinie</SPAN>
<P><SPAN id="msg3" class="error" lang="fr">Erreur de syntaxe pour variable</SPA
N>
The following CSS style rules would tell visual user agents to display
informational messages in green, warning messages in yellow, and error
messages in red:
SPAN.info { color: green }
SPAN.warning { color: yellow }
SPAN.error { color: red }
Note that the French "msg1" and the English "msg1" may not appear in
the same document since they share the same id value. Authors may make
further use of the id attribute to refine the presentation of
individual messages, make them target anchors, etc.
Almost every HTML element may be assigned identifier and class
information.
Suppose, for example, that we are writing a document about a
programming language. The document is to include a number of
preformatted examples. We use the PRE element to format the examples.
We also assign a background color (green) to all instances of the PRE
element belonging to the class "example".
<HEAD>
<TITLE>... document title ...</TITLE>
<STYLE type="text/css">
PRE.example { background : green }
</STYLE>
</HEAD>
<BODY>
<PRE class="example" id="example-1">
...example code here...
</PRE>
</BODY>
By setting the id attribute for this example, we can (1) create a
hyperlink to it and (2) override class style information with instance
style information.
Note. The id attribute shares the same name space as the name
attribute when used for anchor names. Please consult the section on
anchors with id for more information.
7.5.3 Block-level and inline elements
Certain HTML elements that may appear in BODY are said to be
"block-level" while others are "inline" (also known as "text level").
The distinction is founded on several notions:
Content model
Generally, block-level elements may contain inline elements and
other block-level elements. Generally, inline elements may
contain only data and other inline elements. Inherent in this
structural distinction is the idea that block elements create
"larger" structures than inline elements.
Formatting
By default, block-level elements are formatted differently than
inline elements. Generally, block-level elements begin on new
lines, inline elements do not. For information about white
space, line breaks, and block formatting, please consult the
section on text.
Directionality
For technical reasons involving the [UNICODE] bidirectional
text algorithm, block-level and inline elements differ in how
they inherit directionality information. For details, see the
section on inheritance of text direction.
Style sheets provide the means to specify the rendering of arbitrary
elements, including whether an element is rendered as block or inline.
In some cases, such as an inline style for list elements, this may be
appropriate, but generally speaking, authors are discouraged from
overriding the conventional interpretation of HTML elements in this
way.
The alteration of the traditional presentation idioms for block level
and inline elements also has an impact on the bidirectional text
algorithm. See the section on the effect of style sheets on
bidirectionality for more information.
7.5.4 Grouping elements: the DIV and SPAN elements
<!ELEMENT DIV - - (%flow;)* -- generic language/style container -->
<!ATTLIST DIV
%attrs; -- %coreattrs, %i18n, %events --
>
<!ELEMENT SPAN - - (%inline;)* -- generic language/style container -->
<!ATTLIST SPAN
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: required
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* align (alignment)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
The DIV and SPAN elements, in conjunction with the id and class
attributes, offer a generic mechanism for adding structure to
documents. These elements define content to be inline (SPAN) or
block-level (DIV) but impose no other presentational idioms on the
content. Thus, authors may use these elements in conjunction with
style sheets, the lang attribute, etc., to tailor HTML to their own
needs and tastes.
Suppose, for example, that we wanted to generate an HTML document
based on a database of client information. Since HTML does not include
elements that identify objects such as "client", "telephone number",
"email address", etc., we use DIV and SPAN to achieve the desired
structural and presentational effects. We might use the TABLE element
as follows to structure the information:
<!-- Example of data from the client database: -->
<!-- Name: Stephane Boyera, Tel: (212) 555-1212, Email: sb@foo.org -->
<DIV id="client-boyera" class="client">
<P><SPAN class="client-title">Client information:</SPAN>
<TABLE class="client-data">
<TR><TH>Last name:<TD>Boyera</TR>
<TR><TH>First name:<TD>Stephane</TR>
<TR><TH>Tel:<TD>(212) 555-1212</TR>
<TR><TH>Email:<TD>sb@foo.org</TR>
</TABLE>
</DIV>
<DIV id="client-lafon" class="client">
<P><SPAN class="client-title">Client information:</SPAN>
<TABLE class="client-data">
<TR><TH>Last name:<TD>Lafon</TR>
<TR><TH>First name:<TD>Yves</TR>
<TR><TH>Tel:<TD>(617) 555-1212</TR>
<TR><TH>Email:<TD>yves@coucou.com</TR>
</TABLE>
</DIV>
Later, we may easily add style sheet declarations to fine tune the
presentation of these database entries.
For another example of usage, please consult the example in the
section on the class and id attributes.
Visual user agents generally place a line break before and after DIV
elements, for instance:
<P>aaaaaaaaa<DIV>bbbbbbbbb</DIV><DIV>ccccc<P>ccccc</DIV>
which is typically rendered as:
aaaaaaaaa
bbbbbbbbb
ccccc
ccccc
7.5.5 Headings: The H1, H2, H3, H4, H5, H6 elements
<!ENTITY % heading "H1|H2|H3|H4|H5|H6">
<!--
There are six levels of headings from H1 (the most important)
to H6 (the least important).
-->
<!ELEMENT (%heading;) - - (%inline;)* -- heading -->
<!ATTLIST (%heading;)
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: required
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* align (alignment)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
A heading element briefly describes the topic of the section it
introduces. Heading information may be used by user agents, for
example, to construct a table of contents for a document
automatically.
There are six levels of headings in HTML with H1 as the most important
and H6 as the least. Visual browsers usually render more important
headings in larger fonts than less important ones.
The following example shows how to use the DIV element to associate a
heading with the document section that follows it. Doing so allows you
to define a style for the section (color the background, set the font,
etc.) with style sheets.
<DIV class="section" id="forest-elephants" >
<H1>Forest elephants</H1>
<P>In this section, we discuss the lesser known forest elephants.
...this section continues...
<DIV class="subsection" id="forest-habitat" >
<H2>Habitat</H2>
<P>Forest elephants do not live in trees but among them.
...this subsection continues...
</DIV>
</DIV>
This structure may be decorated with style information such as:
<HEAD>
<TITLE>... document title ...</TITLE>
<STYLE type="text/css">
DIV.section { text-align: justify; font-size: 12pt}
DIV.subsection { text-indent: 2em }
H1 { font-style: italic; color: green }
H2 { color: green }
</STYLE>
</HEAD>
Numbered sections and references
HTML does not itself cause section numbers to be generated from
headings. This facility may be offered by user agents, however. Soon,
style sheet languages such as CSS will allow authors to control the
generation of section numbers (handy for forward references in printed
documents, as in "See section 7.2").
Some people consider skipping heading levels to be bad practice. They
accept H1 H2 H1 while they do not accept H1 H3 H1 since the heading
level H2 is skipped.
7.5.6 The ADDRESS element
<!ELEMENT ADDRESS - - (%inline;)* -- information on author -->
<!ATTLIST ADDRESS
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: required
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
The ADDRESS element may be used by authors to supply contact
information for a document or a major part of a document such as a
form. This element often appears at the beginning or end of a
document.
For example, a page at the W3C Web site related to HTML might include
the following contact information:
<ADDRESS>
<A href="../People/Raggett/">Dave Raggett</A>,
<A href="../People/Arnaud/">Arnaud Le Hors</A>,
contact persons for the <A href="Activity">W3C HTML Activity</A><BR>
$Date: 1999/12/24 23:37:46 $
</ADDRESS>
8 Language information and text direction
Contents
1. Specifying the language of content: the lang attribute
1. Language codes
2. Inheritance of language codes
3. Interpretation of language codes
2. Specifying the direction of text and tables: the dir attribute
1. Introduction to the bidirectional algorithm
2. Inheritance of text direction information
3. Setting the direction of embedded text
4. Overriding the bidirectional algorithm: the BDO element
5. Character references for directionality and joining control
6. The effect of style sheets on bidirectionality
This section of the document discusses two important issues that
affect the internationalization of HTML: specifying the language (the
lang attribute) and direction (the dir attribute) of text in a
document.
8.1 Specifying the language of content: the lang attribute
Attribute definitions
lang = language-code [CI]
This attribute specifies the base language of an element's
attribute values and text content. The default value of this
attribute is unknown.
Language information specified via the lang attribute may be used by a
user agent to control rendering in a variety of ways. Some situations
where author-supplied language information may be helpful include:
* Assisting search engines
* Assisting speech synthesizers
* Helping a user agent select glyph variants for high quality
typography
* Helping a user agent choose a set of quotation marks
* Helping a user agent make decisions about hyphenation, ligatures,
and spacing
* Assisting spell checkers and grammar checkers
The lang attribute specifies the language of element content and
attribute values; whether it is relevant for a given attribute depends
on the syntax and semantics of the attribute and the operation
involved.
The intent of the lang attribute is to allow user agents to render
content more meaningfully based on accepted cultural practice for a
given language. This does not imply that user agents should render
characters that are atypical for a particular language in less
meaningful ways; user agents must make a best attempt to render all
characters, regardless of the value specified by lang.
For instance, if characters from the Greek alphabet appear in the
midst of English text:
<P><Q lang="en">Her super-powers were the result of
γ-radiation,</Q> he explained.</P>
a user agent (1) should try to render the English content in an
appropriate manner (e.g., in its handling the quotation marks) and (2)
must make a best attempt to render g even though it is not an English
character.
Please consult the section on undisplayable characters for related
information.
8.1.1 Language codes
The lang attribute's value is a language code that identifies a
natural language spoken, written, or otherwise used for the
communication of information among people. Computer languages are
explicitly excluded from language codes.
[RFC1766] defines and explains the language codes that must be used in
HTML documents.
Briefly, language codes consist of a primary code and a possibly empty
series of subcodes:
language-code = primary-code ( "-" subcode )*
Here are some sample language codes:
* "en": English
* "en-US": the U.S. version of English.
* "en-cockney": the Cockney version of English.
* "i-navajo": the Navajo language spoken by some Native Americans.
* "x-klingon": The primary tag "x" indicates an experimental
language tag
Two-letter primary codes are reserved for [ISO639] language
abbreviations. Two-letter codes include fr (French), de (German), it
(Italian), nl (Dutch), el (Greek), es (Spanish), pt (Portuguese), ar
(Arabic), he (Hebrew), ru (Russian), zh (Chinese), ja (Japanese), hi
(Hindi), ur (Urdu), and sa (Sanskrit).
Any two-letter subcode is understood to be a [ISO3166] country code.
8.1.2 Inheritance of language codes
An element inherits language code information according to the
following order of precedence (highest to lowest):
* The lang attribute set for the element itself.
* The closest parent element that has the lang attribute set (i.e.,
the lang attribute is inherited).
* The HTTP "Content-Language" header (which may be configured in a
server). For example:
Content-Language: en-cockney
* User agent default values and user preferences.
In this example, the primary language of the document is French
("fr"). One paragraph is declared to be in Spanish ("es"), after which
the primary language returns to French. The following paragraph
includes an embedded Japanese ("ja") phrase, after which the primary
language returns to French.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML lang="fr">
<HEAD>
<TITLE>Un document multilingue</TITLE>
</HEAD>
<BODY>
...Interpreted as French...
<P lang="es">...Interpreted as Spanish...
<P>...Interpreted as French again...
<P>...French text interrupted by<EM lang="ja">some
Japanese</EM>French begins here again...
</BODY>
</HTML>
Note. Table cells may inherit lang values not from its parent but from
the first cell in a span. Please consult the section on alignment
inheritance for details.
8.1.3 Interpretation of language codes
In the context of HTML, a language code should be interpreted by user
agents as a hierarchy of tokens rather than a single token. When a
user agent adjusts rendering according to language information (say,
by comparing style sheet language codes and lang values), it should
always favor an exact match, but should also consider matching primary
codes to be sufficient. Thus, if the lang attribute value of "en-US"
is set for the HTML element, a user agent should prefer style
information that matches "en-US" first, then the more general value
"en".
Note. Language code hierarchies do not guarantee that all languages
with a common prefix will be understood by those fluent in one or more
of those languages. They do allow a user to request this commonality
when it is true for that user.
8.2 Specifying the direction of text and tables: the dir attribute
Attribute definitions
dir = LTR | RTL [CI]
This attribute specifies the base direction of directionally
neutral text (i.e., text that doesn't have inherent
directionality as defined in [UNICODE]) in an element's content
and attribute values. It also specifies the directionality of
tables. Possible values:
+ LTR: Left-to-right text or table.
+ RTL: Right-to-left text or table.
In addition to specifying the language of a document with the lang
attribute, authors may need to specify the base directionality
(left-to-right or right-to-left) of portions of a document's text, of
table structure, etc. This is done with the dir attribute.
The [UNICODE] specification assigns directionality to characters and
defines a (complex) algorithm for determining the proper
directionality of text. If a document does not contain a displayable
right-to-left character, a conforming user agent is not required to
apply the [UNICODE] bidirectional algorithm. If a document contains
right-to-left characters, and if the user agent displays these
characters, the user agent must use the bidirectional algorithm.
Although Unicode specifies special characters that deal with text
direction, HTML offers higher-level markup constructs that do the same
thing: the dir attribute (do not confuse with the DIR element) and the
BDO element. Thus, to express a Hebrew quotation, it is more intuitive
to write
<Q lang="he" dir="rtl">...a Hebrew quotation...</Q>
than the equivalent with Unicode references:
‫״...a Hebrew quotation...״‬
User agents must not use the lang attribute to determine text
directionality.
The dir attribute is inherited and may be overridden. Please consult
the section on the inheritance of text direction information for
details.
8.2.1 Introduction to the bidirectional algorithm
The following example illustrates the expected behavior of the
bidirectional algorithm. It involves English, a left-to-right script,
and Hebrew, a right-to-left script.
Consider the following example text:
english1 HEBREW2 english3 HEBREW4 english5 HEBREW6
The characters in this example (and in all related examples) are
stored in the computer the way they are displayed here: the first
character in the file is "e", the second is "n", and the last is "6".
Suppose the predominant language of the document containing this
paragraph is English. This means that the base direction is
left-to-right. The correct presentation of this line would be:
english1 2WERBEH english3 4WERBEH english5 6WERBEH
<------ <------ <------
H H H
------------------------------------------------->
E
The dotted lines indicate the structure of the sentence: English
predominates and some Hebrew text is embedded. Achieving the correct
presentation requires no additional markup since the Hebrew fragments
are reversed correctly by user agents applying the bidirectional
algorithm.
If, on the other hand, the predominant language of the document is
Hebrew, the base direction is right-to-left. The correct presentation
is therefore:
6WERBEH english5 4WERBEH english3 2WERBEH english1
-------> -------> ------->
E E E
<-------------------------------------------------
H
In this case, the whole sentence has been presented as right-to-left
and the embedded English sequences have been properly reversed by the
bidirectional algorithm.
8.2.2 Inheritance of text direction information
The Unicode bidirectional algorithm requires a base text direction for
text blocks. To specify the base direction of a block-level element,
set the element's dir attribute. The default value of the dir
attribute is "ltr" (left-to-right text).
When the dir attribute is set for a block-level element, it remains in
effect for the duration of the element and any nested block-level
elements. Setting the dir attribute on a nested element overrides the
inherited value.
To set the base text direction for an entire document, set the dir
attribute on the HTML element.
For example:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML dir="RTL">
<HEAD>
<TITLE>...a right-to-left title...</TITLE>
</HEAD>
...right-to-left text...
<P dir="ltr">...left-to-right text...</P>
<P>...right-to-left text again...</P>
</HTML>
Inline elements, on the other hand, do not inherit the dir attribute.
This means that an inline element without a dir attribute does not
open an additional level of embedding with respect to the
bidirectional algorithm. (Here, an element is considered to be
block-level or inline based on its default presentation. Note that the
INS and DEL elements can be block-level or inline depending on their
context.)
8.2.3 Setting the direction of embedded text
The [UNICODE] bidirectional algorithm automatically reverses embedded
character sequences according to their inherent directionality (as
illustrated by the previous examples). However, in general only one
level of embedding can be accounted for. To achieve additional levels
of embedded direction changes, you must make use of the dir attribute
on an inline element.
Consider the same example text as before:
english1 HEBREW2 english3 HEBREW4 english5 HEBREW6
Suppose the predominant language of the document containing this
paragraph is English. Furthermore, the above English sentence contains
a Hebrew section extending from HEBREW2 through HEBREW4 and the Hebrew
section contains an English quotation (english3). The desired
presentation of the text is thus:
english1 4WERBEH english3 2WERBEH english5 6WERBEH
------->
E
<-----------------------
H
------------------------------------------------->
E
To achieve two embedded direction changes, we must supply additional
information, which we do by delimiting the second embedding
explicitly. In this example, we use the SPAN element and the dir
attribute to mark up the text:
english1 <SPAN dir="RTL">HEBREW2 english3 HEBREW4</SPAN> english5 HEBREW6
Authors may also use special Unicode characters to achieve multiple
embedded direction changes. To achieve left-to-right embedding,
surround embedded text with the characters LEFT-TO-RIGHT EMBEDDING
("LRE", hexadecimal 202A) and POP DIRECTIONAL FORMATTING ("PDF",
hexadecimal 202C). To achieve right-to-left embedding, surround
embedded text with the characters RIGHT-TO-LEFT EMBEDDING ("RTE",
hexadecimal 202B) and PDF.
Using HTML directionality markup with Unicode characters. Authors and
designers of authoring software should be aware that conflicts can
arise if the dir attribute is used on inline elements (including BDO)
concurrently with the corresponding [UNICODE] formatting characters.
Preferably one or the other should be used exclusively. The markup
method offers a better guarantee of document structural integrity and
alleviates some problems when editing bidirectional HTML text with a
simple text editor, but some software may be more apt at using the
[UNICODE] characters. If both methods are used, great care should be
exercised to insure proper nesting of markup and directional embedding
or override, otherwise, rendering results are undefined.
8.2.4 Overriding the bidirectional algorithm: the BDO element
<!ELEMENT BDO - - (%inline;)* -- I18N BiDi over-ride -->
<!ATTLIST BDO
%coreattrs; -- id, class, style, title --
lang %LanguageCode; #IMPLIED -- language code --
dir (ltr|rtl) #REQUIRED -- directionality --
>
Start tag: required, End tag: required
Attribute definitions
dir = LTR | RTL [CI]
This mandatory attribute specifies the base direction of the
element's text content. This direction overrides the inherent
directionality of characters as defined in [UNICODE]. Possible
values:
+ LTR: Left-to-right text.
+ RTL: Right-to-left text.
Attributes defined elsewhere
* lang (language information)
The bidirectional algorithm and the dir attribute generally suffice to
manage embedded direction changes. However, some situations may arise
when the bidirectional algorithm results in incorrect presentation.
The BDO element allows authors to turn off the bidirectional algorithm
for selected fragments of text.
Consider a document containing the same text as before:
english1 HEBREW2 english3 HEBREW4 english5 HEBREW6
but assume that this text has already been put in visual order. One
reason for this may be that the MIME standard ([RFC2045], [RFC1556])
favors visual order, i.e., that right-to-left character sequences are
inserted right-to-left in the byte stream. In an email, the above
might be formatted, including line breaks, as:
english1 2WERBEH english3
4WERBEH english5 6WERBEH
This conflicts with the [UNICODE] bidirectional algorithm, because
that algorithm would invert 2WERBEH, 4WERBEH, and 6WERBEH a second
time, displaying the Hebrew words left-to-right instead of
right-to-left.
The solution in this case is to override the bidirectional algorithm
by putting the Email excerpt in a PRE element (to conserve line
breaks) and each line in a BDO element, whose dir attribute is set to
LTR:
<PRE>
<BDO dir="LTR">english1 2WERBEH english3</BDO>
<BDO dir="LTR">4WERBEH english5 6WERBEH</BDO>
</PRE>
This tells the bidirectional algorithm "Leave me left-to-right!" and
would produce the desired presentation:
english1 2WERBEH english3
4WERBEH english5 6WERBEH
The BDO element should be used in scenarios where absolute control
over sequence order is required (e.g., multi-language part numbers).
The dir attribute is mandatory for this element.
Authors may also use special Unicode characters to override the
bidirectional algorithm -- LEFT-TO-RIGHT OVERRIDE (202D) or
RIGHT-TO-LEFT OVERRIDE (hexadecimal 202E). The POP DIRECTIONAL
FORMATTING (hexadecimal 202C) character ends either bidirectional
override.
Note. Recall that conflicts can arise if the dir attribute is used on
inline elements (including BDO) concurrently with the corresponding
[UNICODE] formatting characters.
Bidirectionality and character encoding According to [RFC1555] and
[RFC1556], there are special conventions for the use of "charset"
parameter values to indicate bidirectional treatment in MIME mail, in
particular to distinguish between visual, implicit, and explicit
directionality. The parameter value "ISO-8859-8" (for Hebrew) denotes
visual encoding, "ISO-8859-8-i" denotes implicit bidirectionality, and
"ISO-8859-8-e" denotes explicit directionality.
Because HTML uses the Unicode bidirectionality algorithm, conforming
documents encoded using ISO 8859-8 must be labeled as "ISO-8859-8-i".
Explicit directional control is also possible with HTML, but cannot be
expressed with ISO 8859-8, so "ISO-8859-8-e" should not be used.
The value "ISO-8859-8" implies that the document is formatted
visually, misusing some markup (such as TABLE with right alignment and
no line wrapping) to ensure reasonable display on older user agents
that do not handle bidirectionality. Such documents do not conform to
the present specification. If necessary, they can be made to conform
to the current specification (and at the same time will be displayed
correctly on older user agents) by adding BDO markup where necessary.
Contrary to what is said in [RFC1555] and [RFC1556], ISO-8859-6
(Arabic) is not visual ordering.
8.2.5 Character references for directionality and joining control
Since ambiguities sometimes arise as to the directionality of certain
characters (e.g., punctuation), the [UNICODE] specification includes
characters to enable their proper resolution. Also, Unicode includes
some characters to control joining behavior where this is necessary
(e.g., some situations with Arabic letters). HTML 4 includes character
references for these characters.
The following DTD excerpt presents some of the directional entities:
<!ENTITY zwnj CDATA "‌"--=zero width non-joiner-->
<!ENTITY zwj CDATA "‍"--=zero width joiner-->
<!ENTITY lrm CDATA "‎"--=left-to-right mark-->
<!ENTITY rlm CDATA "‏"--=right-to-left mark-->
The zwnj entity is used to block joining behavior in contexts where
joining will occur but shouldn't. The zwj entity does the opposite; it
forces joining when it wouldn't occur but should. For example, the
Arabic letter "HEH" is used to abbreviate "Hijri", the name of the
Islamic calendar system. Since the isolated form of "HEH" looks like
the digit five as employed in Arabic script (based on Indic digits),
in order to prevent confusing "HEH" as a final digit five in a year,
the initial form of "HEH" is used. However, there is no following
context (i.e., a joining letter) to which the "HEH" can join. The zwj
character provides that context.
Similarly, in Persian texts, there are cases where a letter that
normally would join a subsequent letter in a cursive connection should
not. The character zwnj is used to block joining in such cases.
The other characters, lrm and rlm, are used to force directionality of
directionally neutral characters. For example, if a double quotation
mark comes between an Arabic (right-to-left) and a Latin
(left-to-right) letter, the direction of the quotation mark is not
clear (is it quoting the Arabic text or the Latin text?). The lrm and
rlm characters have a directional property but no width and no
word/line break property. Please consult [UNICODE] for more details.
Mirrored character glyphs. In general, the bidirectional algorithm
does not mirror character glyphs but leaves them unaffected. An
exception are characters such as parentheses (see [UNICODE], table
4-7). In cases where mirroring is desired, for example for Egyptian
Hieroglyphs, Greek Bustrophedon, or special design effects, this
should be controlled with styles.
8.2.6 The effect of style sheets on bidirectionality
In general, using style sheets to change an element's visual rendering
from block-level to inline or vice-versa is straightforward. However,
because the bidirectional algorithm relies on the inline/block-level
distinction, special care must be taken during the transformation.
When an inline element that does not have a dir attribute is
transformed to the style of a block-level element by a style sheet, it
inherits the dir attribute from its closest parent block element to
define the base direction of the block.
When a block element that does not have a dir attribute is transformed
to the style of an inline element by a style sheet, the resulting
presentation should be equivalent, in terms of bidirectional
formatting, to the formatting obtained by explicitly adding a dir
attribute (assigned the inherited value) to the transformed element.
9 Text
Contents
1. White space
2. Structured text
1. Phrase elements: EM, STRONG, DFN, CODE, SAMP, KBD, VAR, CITE,
ABBR, and ACRONYM
2. Quotations: The BLOCKQUOTE and Q elements
o Rendering quotations
3. Subscripts and superscripts: the SUB and SUP elements
3. Lines and Paragraphs
1. Paragraphs: the P element
2. Controlling line breaks
o Forcing a line break: the BR element
o Prohibiting a line break
3. Hyphenation
4. Preformatted text: The PRE element
5. Visual rendering of paragraphs
4. Marking document changes: The INS and DEL elements
The following sections discuss issues surrounding the structuring of
text. Elements that present text (alignment elements, font elements,
style sheets, etc.) are discussed elsewhere in the specification. For
information about characters, please consult the section on the
document character set.
9.1 White space
The document character set includes a wide variety of white space
characters. Many of these are typographic elements used in some
applications to produce particular visual spacing effects. In HTML,
only the following characters are defined as white space characters:
* ASCII space ( )
* ASCII tab (	)
* ASCII form feed ()
* Zero-width space (​)
Line breaks are also white space characters. Note that although

 and 
 are defined in [ISO10646] to unambiguously
separate lines and paragraphs, respectively, these do not constitute
line breaks in HTML, nor does this specification include them in the
more general category of white space characters.
This specification does not indicate the behavior, rendering or
otherwise, of space characters other than those explicitly identified
here as white space characters. For this reason, authors should use
appropriate elements and styles to achieve visual formatting effects
that involve white space, rather than space characters.
For all HTML elements except PRE, sequences of white space separate
"words" (we use the term "word" here to mean "sequences of non-white
space characters"). When formatting text, user agents should identify
these words and lay them out according to the conventions of the
particular written language (script) and target medium.
This layout may involve putting space between words (called inter-word
space), but conventions for inter-word space vary from script to
script. For example, in Latin scripts, inter-word space is typically
rendered as an ASCII space ( ), while in Thai it is a
zero-width word separator (​). In Japanese and Chinese,
inter-word space is not typically rendered at all.
Note that a sequence of white spaces between words in the source
document may result in an entirely different rendered inter-word
spacing (except in the case of the PRE element). In particular, user
agents should collapse input white space sequences when producing
output inter-word space. This can and should be done even in the
absence of language information (from the lang attribute, the HTTP
"Content-Language" header field (see [RFC2616], section 14.12), user
agent settings, etc.).
The PRE element is used for preformatted text, where white space is
significant.
In order to avoid problems with SGML line break rules and
inconsistencies among extant implementations, authors should not rely
on user agents to render white space immediately after a start tag or
immediately before an end tag. Thus, authors, and in particular
authoring tools, should write:
<P>We offer free <A>technical support</A> for subscribers.</P>
and not:
<P>We offer free<A> technical support </A>for subscribers.</P>
9.2 Structured text
9.2.1 Phrase elements: EM, STRONG, DFN, CODE, SAMP, KBD, VAR, CITE, ABBR, and
ACRONYM
<!ENTITY % phrase "EM | STRONG | DFN | CODE |
SAMP | KBD | VAR | CITE | ABBR | ACRONYM" >
<!ELEMENT (%fontstyle;|%phrase;) - - (%inline;)*>
<!ATTLIST (%fontstyle;|%phrase;)
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: required
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events )
Phrase elements add structural information to text fragments. The
usual meanings of phrase elements are following:
EM:
Indicates emphasis.
STRONG:
Indicates stronger emphasis.
CITE:
Contains a citation or a reference to other sources.
DFN:
Indicates that this is the defining instance of the enclosed
term.
CODE:
Designates a fragment of computer code.
SAMP:
Designates sample output from programs, scripts, etc.
KBD:
Indicates text to be entered by the user.
VAR:
Indicates an instance of a variable or program argument.
ABBR:
Indicates an abbreviated form (e.g., WWW, HTTP, URI, Mass.,
etc.).
ACRONYM:
Indicates an acronym (e.g., WAC, radar, etc.).
EM and STRONG are used to indicate emphasis. The other phrase elements
have particular significance in technical documents. These examples
illustrate some of the phrase elements:
As <CITE>Harry S. Truman</CITE> said,
<Q lang="en-us">The buck stops here.</Q>
More information can be found in <CITE>[ISO-0000]</CITE>.
Please refer to the following reference number in future
correspondence: <STRONG>1-234-55</STRONG>
The presentation of phrase elements depends on the user agent.
Generally, visual user agents present EM text in italics and STRONG
text in bold font. Speech synthesizer user agents may change the
synthesis parameters, such as volume, pitch and rate accordingly.
The ABBR and ACRONYM elements allow authors to clearly indicate
occurrences of abbreviations and acronyms. Western languages make
extensive use of acronyms such as "GmbH", "NATO", and "F.B.I.", as
well as abbreviations like "M.", "Inc.", "et al.", "etc.". Both
Chinese and Japanese use analogous abbreviation mechanisms, wherein a
long name is referred to subsequently with a subset of the Han
characters from the original occurrence. Marking up these constructs
provides useful information to user agents and tools such as spell
checkers, speech synthesizers, translation systems and search-engine
indexers.
The content of the ABBR and ACRONYM elements specifies the abbreviated
expression itself, as it would normally appear in running text. The
title attribute of these elements may be used to provide the full or
expanded form of the expression.
Here are some sample uses of ABBR:
<P>
<ABBR title="World Wide Web">WWW</ABBR>
<ABBR lang="fr"
title="Société Nationale des Chemins de Fer">
SNCF
</ABBR>
<ABBR lang="es" title="Doña">Doña</ABBR>
<ABBR title="Abbreviation">abbr.</ABBR>
Note that abbreviations and acronyms often have idiosyncratic
pronunciations. For example, while "IRS" and "BBC" are typically
pronounced letter by letter, "NATO" and "UNESCO" are pronounced
phonetically. Still other abbreviated forms (e.g., "URI" and "SQL")
are spelled out by some people and pronounced as words by other
people. When necessary, authors should use style sheets to specify the
pronunciation of an abbreviated form.
9.2.2 Quotations: The BLOCKQUOTE and Q elements
<!ELEMENT BLOCKQUOTE - - (%block;|SCRIPT)+ -- long quotation -->
<!ATTLIST BLOCKQUOTE
%attrs; -- %coreattrs, %i18n, %events --
cite %URI; #IMPLIED -- URI for source document or msg --
>
<!ELEMENT Q - - (%inline;)* -- short inline quotation -->
<!ATTLIST Q
%attrs; -- %coreattrs, %i18n, %events --
cite %URI; #IMPLIED -- URI for source document or msg --
>
Start tag: required, End tag: required
Attribute definitions
cite = uri [CT]
The value of this attribute is a URI that designates a source
document or message. This attribute is intended to give
information about the source from which the quotation was
borrowed.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events )
These two elements designate quoted text. BLOCKQUOTE is for long
quotations (block-level content) and Q is intended for short
quotations (inline content) that don't require paragraph breaks.
This example formats an excerpt from "The Two Towers", by J.R.R.
Tolkien, as a blockquote.
<BLOCKQUOTE cite="http://www.mycom.com/tolkien/twotowers.html">
<P>They went in single file, running like hounds on a strong scent,
and an eager light was in their eyes. Nearly due west the broad
swath of the marching Orcs tramped its ugly slot; the sweet grass
of Rohan had been bruised and blackened as they passed.</P>
</BLOCKQUOTE>
Rendering quotations
Visual user agents generally render BLOCKQUOTE as an indented block.
Visual user agents must ensure that the content of the Q element is
rendered with delimiting quotation marks. Authors should not put
quotation marks at the beginning and end of the content of a Q
element.
User agents should render quotation marks in a language-sensitive
manner (see the lang attribute). Many languages adopt different
quotation styles for outer and inner (nested) quotations, which should
be respected by user-agents.
The following example illustrates nested quotations with the Q
element.
John said, <Q lang="en-us">I saw Lucy at lunch, she told me
<Q lang="en-us">Mary wants you
to get some ice cream on your way home.</Q> I think I will get
some at Ben and Jerry's, on Gloucester Road.</Q>
Since the language of both quotations is American English, user agents
should render them appropriately, for example with single quote marks
around the inner quotation and double quote marks around the outer
quotation:
John said, "I saw Lucy at lunch, she told me 'Mary wants you
to get some ice cream on your way home.' I think I will get some
at Ben and Jerry's, on Gloucester Road."
Note. We recommend that style sheet implementations provide a
mechanism for inserting quotation marks before and after a quotation
delimited by BLOCKQUOTE in a manner appropriate to the current
language context and the degree of nesting of quotations.
However, as some authors have used BLOCKQUOTE merely as a mechanism to
indent text, in order to preserve the intention of the authors, user
agents should not insert quotation marks in the default style.
The usage of BLOCKQUOTE to indent text is deprecated in favor of style
sheets.
9.2.3 Subscripts and superscripts: the SUB and SUP elements
<!ELEMENT (SUB|SUP) - - (%inline;)* -- subscript, superscript -->
<!ATTLIST (SUB|SUP)
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: required
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events )
Many scripts (e.g., French) require superscripts or subscripts for
proper rendering. The SUB and SUP elements should be used to markup
text in these cases.
H<sub>2</sub>O
E = mc<sup>2</sup>
<SPAN lang="fr">M<sup>lle</sup> Dupont</SPAN>
9.3 Lines and Paragraphs
Authors traditionally divide their thoughts and arguments into
sequences of paragraphs. The organization of information into
paragraphs is not affected by how the paragraphs are presented:
paragraphs that are double-justified contain the same thoughts as
those that are left-justified.
The HTML markup for defining a paragraph is straightforward: the P
element defines a paragraph.
The visual presentation of paragraphs is not so simple. A number of
issues, both stylistic and technical, must be addressed:
* Treatment of white space
* Line breaking and word wrapping
* Justification
* Hyphenation
* Written language conventions and text directionality
* Formatting of paragraphs with respect to surrounding content
We address these questions below. Paragraph alignment and floating
objects are discussed later in this document.
9.3.1 Paragraphs: the P element
<!ELEMENT P - O (%inline;)* -- paragraph -->
<!ATTLIST P
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: optional
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* align (alignment)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events )
The P element represents a paragraph. It cannot contain block-level
elements (including P itself).
We discourage authors from using empty P elements. User agents should
ignore empty P elements.
9.3.2 Controlling line breaks
A line break is defined to be a carriage return (
), a line
feed (
), or a carriage return/line feed pair. All line breaks
constitute white space.
For more information about SGML's specification of line breaks, please
consult the notes on line breaks in the appendix.
Forcing a line break: the BR element
<!ELEMENT BR - O EMPTY -- forced line break -->
<!ATTLIST BR
%coreattrs; -- id, class, style, title --
>
Start tag: required, End tag: forbidden
Attributes defined elsewhere
* id, class (document-wide identifiers)
* title (element title)
* style (inline style information )
* clear (alignment and floating objects )
The BR element forcibly breaks (ends) the current line of text.
For visual user agents, the clear attribute can be used to determine
whether markup following the BR element flows around images and other
objects floated to the left or right margin, or whether it starts
after the bottom of such objects. Further details are given in the
section on alignment and floating objects. Authors are advised to use
style sheets to control text flow around floating images and other
objects.
With respect to bidirectional formatting, the BR element should behave
the same way the [ISO10646] LINE SEPARATOR character behaves in the
bidirectional algorithm.
Prohibiting a line break
Sometimes authors may want to prevent a line break from occurring
between two words. The entity (  or  ) acts as a
space where user agents should not cause a line break.
9.3.3 Hyphenation
In HTML, there are two types of hyphens: the plain hyphen and the soft
hyphen. The plain hyphen should be interpreted by a user agent as just
another character. The soft hyphen tells the user agent where a line
break can occur.
Those browsers that interpret soft hyphens must observe the following
semantics: If a line is broken at a soft hyphen, a hyphen character
must be displayed at the end of the first line. If a line is not
broken at a soft hyphen, the user agent must not display a hyphen
character. For operations such as searching and sorting, the soft
hyphen should always be ignored.
In HTML, the plain hyphen is represented by the "-" character (-
or -). The soft hyphen is represented by the character entity
reference ­ (­ or ­)
9.3.4 Preformatted text: The PRE element
<!ENTITY % pre.exclusion "IMG|OBJECT|BIG|SMALL|SUB|SUP">
<!ELEMENT PRE - - (%inline;)* -(%pre.exclusion;) -- preformatted text -->
<!ATTLIST PRE
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: required
Attribute definitions
width = number [CN]
Deprecated. This attribute provides a hint to visual user
agents about the desired width of the formatted block. The user
agent can use this information to select an appropriate font
size or to indent the content appropriately. The desired width
is expressed in number of characters. This attribute is not
widely supported currently.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events )
The PRE element tells visual user agents that the enclosed text is
"preformatted". When handling preformatted text, visual user agents:
* May leave white space intact.
* May render text with a fixed-pitch font.
* May disable automatic word wrap.
* Must not disable bidirectional processing.
Non-visual user agents are not required to respect extra white space
in the content of a PRE element.
For more information about SGML's specification of line breaks, please
consult the notes on line breaks in the appendix.
The DTD fragment above indicates which elements may not appear within
a PRE declaration. This is the same as in HTML 3.2, and is intended to
preserve constant line spacing and column alignment for text rendered
in a fixed pitch font. Authors are discouraged from altering this
behavior through style sheets.
The following example shows a preformatted verse from Shelly's poem To
a Skylark:
<PRE>
Higher still and higher
From the earth thou springest
Like a cloud of fire;
The blue deep thou wingest,
And singing still dost soar, and soaring ever singest.
</PRE>
Here is how this is typically rendered:
Higher still and higher
From the earth thou springest
Like a cloud of fire;
The blue deep thou wingest,
And singing still dost soar, and soaring ever singest.
The horizontal tab character
The horizontal tab character (decimal 9 in [ISO10646] and [ISO88591] )
is usually interpreted by visual user agents as the smallest non-zero
number of spaces necessary to line characters up along tab stops that
are every 8 characters. We strongly discourage using horizontal tabs
in preformatted text since it is common practice, when editing, to set
the tab-spacing to other values, leading to misaligned documents.
9.3.5 Visual rendering of paragraphs
Note. The following section is an informative description of the
behavior of some current visual user agents when formatting
paragraphs. Style sheets allow better control of paragraph formatting.
How paragraphs are rendered visually depends on the user agent.
Paragraphs are usually rendered flush left with a ragged right margin.
Other defaults are appropriate for right-to-left scripts.
HTML user agents have traditionally rendered paragraphs with white
space before and after, e.g.,
At the same time, there began to take form a system of numbering,
the calendar, hieroglyphic writing, and a technically advanced
art, all of which later influenced other peoples.
Within the framework of this gradual evolution or cultural
progress the Preclassic horizon has been divided into Lower,
Middle and Upper periods, to which can be added a transitional
or Protoclassic period with several features that would later
distinguish the emerging civilizations of Mesoamerica.
This contrasts with the style used in novels which indents the first
line of the paragraph and uses the regular line spacing between the
final line of the current paragraph and the first line of the next,
e.g.,
At the same time, there began to take form a system of
numbering, the calendar, hieroglyphic writing, and a technically
advanced art, all of which later influenced other peoples.
Within the framework of this gradual evolution or cultural
progress the Preclassic horizon has been divided into Lower,
Middle and Upper periods, to which can be added a transitional
or Protoclassic period with several features that would later
distinguish the emerging civilizations of Mesoamerica.
Following the precedent set by the NCSA Mosaic browser in 1993, user
agents generally don't justify both margins, in part because it's hard
to do this effectively without sophisticated hyphenation routines. The
advent of style sheets, and anti-aliased fonts with subpixel
positioning promises to offer richer choices to HTML authors than
previously possible.
Style sheets provide rich control over the size and style of a font,
the margins, space before and after a paragraph, the first line
indent, justification and many other details. The user agent's default
style sheet renders P elements in a familiar form, as illustrated
above. One could, in principle, override this to render paragraphs
without the breaks that conventionally distinguish successive
paragraphs. In general, since this may confuse readers, we discourage
this practice.
By convention, visual HTML user agents wrap text lines to fit within
the available margins. Wrapping algorithms depend on the script being
formatted.
In Western scripts, for example, text should only be wrapped at white
space. Early user agents incorrectly wrapped lines just after the
start tag or just before the end tag of an element, which resulted in
dangling punctuation. For example, consider this sentence:
A statue of the <A href="cih78">Cihuateteus</A>, who are patron ...
Wrapping the line just before the end tag of the A element causes the
comma to be stranded at the beginning of the next line:
A statue of the Cihuateteus
, who are patron ...
This is an error since there was no white space at that point in the
markup.
9.4 Marking document changes: The INS and DEL elements
<!-- INS/DEL are handled by inclusion on BODY -->
<!ELEMENT (INS|DEL) - - (%flow;)* -- inserted text, deleted text -->
<!ATTLIST (INS|DEL)
%attrs; -- %coreattrs, %i18n, %events --
cite %URI; #IMPLIED -- info on reason for change --
datetime %Datetime; #IMPLIED -- date and time of change --
>
Start tag: required, End tag: required
Attribute definitions
cite = uri [CT]
The value of this attribute is a URI that designates a source
document or message. This attribute is intended to point to
information explaining why a document was changed.
datetime = datetime [CS]
The value of this attribute specifies the date and time when
the change was made.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events )
INS and DEL are used to markup sections of the document that have been
inserted or deleted with respect to a different version of a document
(e.g., in draft legislation where lawmakers need to view the changes).
These two elements are unusual for HTML in that they may serve as
either block-level or inline elements (but not both). They may contain
one or more words within a paragraph or contain one or more
block-level elements such as paragraphs, lists and tables.
This example could be from a bill to change the legislation for how
many deputies a County Sheriff can employ from 3 to 5.
<P>
A Sheriff can employ <DEL>3</DEL><INS>5</INS> deputies.
</P>
The INS and DEL elements must not contain block-level content when
these elements behave as inline elements.
ILLEGAL EXAMPLE:
The following is not legal HTML.
<P>
<INS><DIV>...block-level content...</DIV></INS>
</P>
User agents should render inserted and deleted text in ways that make
the change obvious. For instance, inserted text may appear in a
special font, deleted text may not be shown at all or be shown as
struck-through or with special markings, etc.
Both of the following examples correspond to November 5, 1994, 8:15:30
am, US Eastern Standard Time.
1994-11-05T13:15:30Z
1994-11-05T08:15:30-05:00
Used with INS, this gives:
<INS datetime="1994-11-05T08:15:30-05:00"
cite="http://www.foo.org/mydoc/comments.html">
Furthermore, the latest figures from the marketing department
suggest that such practice is on the rise.
</INS>
The document "http://www.foo.org/mydoc/comments.html" would contain
comments about why information was inserted into the document.
Authors may also make comments about inserted or deleted text by means
of the title attribute for the INS and DEL elements. User agents may
present this information to the user (e.g., as a popup note). For
example:
<INS datetime="1994-11-05T08:15:30-05:00"
title="Changed as a result of Steve B's comments in meeting.">
Furthermore, the latest figures from the marketing department
suggest that such practice is on the rise.
</INS>
10 Lists
Contents
1. Introduction to lists
2. Unordered lists (UL), ordered lists (OL), and list items (LI)
3. Definition lists: the DL, DT, and DD elements
1. Visual rendering of lists
4. The DIR and MENU elements
10.1 Introduction to lists
HTML offers authors several mechanisms for specifying lists of
information. All lists must contain one or more list elements. Lists
may contain:
* Unordered information.
* Ordered information.
* Definitions.
The previous list, for example, is an unordered list, created with the
UL element:
<UL>
<LI>Unordered information.
<LI>Ordered information.
<LI>Definitions.
</UL>
An ordered list, created using the OL element, should contain
information where order should be emphasized, as in a recipe:
1. Mix dry ingredients thoroughly.
2. Pour in wet ingredients.
3. Mix for 10 minutes.
4. Bake for one hour at 300 degrees.
Definition lists, created using the DL element, generally consist of a
series of term/definition pairs (although definition lists may have
other applications). Thus, when advertising a product, one might use a
definition list:
Lower cost
The new version of this product costs significantly less than
the previous one!
Easier to use
We've changed the product so that it's much easier to use!
Safe for kids
You can leave your kids alone in a room with this product and
they won't get hurt (not a guarantee).
defined in HTML as:
<DL>
<DT><STRONG>Lower cost</STRONG>
<DD>The new version of this product costs significantly less than the
previous one!
<DT><STRONG>Easier to use</STRONG>
<DD>We've changed the product so that it's much easier to use!
<DT><STRONG>Safe for kids</STRONG>
<DD>You can leave your kids alone in a room with this product and
they won't get hurt (not a guarantee).
</DL>
Lists may also be nested and different list types may be used
together, as in the following example, which is a definition list that
contains an unordered list (the ingredients) and an ordered list (the
procedure):
The ingredients:
+ 100 g. flour
+ 10 g. sugar
+ 1 cup water
+ 2 eggs
+ salt, pepper
The procedure:
1. Mix dry ingredients thoroughly.
2. Pour in wet ingredients.
3. Mix for 10 minutes.
4. Bake for one hour at 300 degrees.
Notes:
The recipe may be improved by adding raisins.
The exact presentation of the three list types depends on the user
agent. We discourage authors from using lists purely as a means of
indenting text. This is a stylistic issue and is properly handled by
style sheets.
10.2 Unordered lists (UL), ordered lists (OL), and list items (LI)
<!ELEMENT UL - - (LI)+ -- unordered list -->
<!ATTLIST UL
%attrs; -- %coreattrs, %i18n, %events --
>
<!ELEMENT OL - - (LI)+ -- ordered list -->
<!ATTLIST OL
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: required
<!ELEMENT LI - O (%flow;)* -- list item -->
<!ATTLIST LI
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: optional
Attribute definitions
type = style-information [CI]
Deprecated. This attribute sets the style of a list item.
Currently available values are intended for visual user agents.
Possible values are described below (along with case
information).
start = number [CN]
Deprecated. For OL only. This attribute specifies the starting
number of the first item in an ordered list. The default
starting number is "1". Note that while the value of this
attribute is an integer, the corresponding label may be
non-numeric. Thus, when the list item style is uppercase latin
letters (A, B, C, ...), start=3 means "C". When the style is
lowercase roman numerals, start=3 means "iii", etc.
value = number [CN]
Deprecated. For LI only. This attribute sets the number of the
current list item. Note that while the value of this attribute
is an integer, the corresponding label may be non-numeric (see
the start attribute).
compact [CI]
Deprecated. When set, this boolean attribute gives a hint to
visual user agents to render the list in a more compact way.
The interpretation of this attribute depends on the user agent.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
Ordered and unordered lists are rendered in an identical manner except
that visual user agents number ordered list items. User agents may
present those numbers in a variety of ways. Unordered list items are
not numbered.
Both types of lists are made up of sequences of list items defined by
the LI element (whose end tag may be omitted).
This example illustrates the basic structure of a list.
<UL>
<LI> ... first list item...
<LI> ... second list item...
...
</UL>
Lists may also be nested:
DEPRECATED EXAMPLE:
<UL>
<LI> ... Level one, number one...
<OL>
<LI> ... Level two, number one...
<LI> ... Level two, number two...
<OL start="10">
<LI> ... Level three, number one...
</OL>
<LI> ... Level two, number three...
</OL>
<LI> ... Level one, number two...
</UL>
Details about number order. In ordered lists, it is not possible to
continue list numbering automatically from a previous list or to hide
numbering of some list items. However, authors can reset the number of
a list item by setting its value attribute. Numbering continues from
the new value for subsequent list items. For example:
<ol>
<li value="30"> makes this list item number 30.
<li value="40"> makes this list item number 40.
<li> makes this list item number 41.
</ol>
10.3 Definition lists: the DL, DT, and DD elements
<!-- definition lists - DT for term, DD for its definition -->
<!ELEMENT DL - - (DT|DD)+ -- definition list -->
<!ATTLIST DL
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: required
<!ELEMENT DT - O (%inline;)* -- definition term -->
<!ELEMENT DD - O (%flow;)* -- definition description -->
<!ATTLIST (DT|DD)
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: optional
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
Definition lists vary only slightly from other types of lists in that
list items consist of two parts: a term and a description. The term is
given by the DT element and is restricted to inline content. The
description is given with a DD element that contains block-level
content.
Here is an example:
<DL>
<DT>Dweeb
<DD>young excitable person who may mature
into a <EM>Nerd</EM> or <EM>Geek</EM>
<DT>Hacker
<DD>a clever programmer
<DT>Nerd
<DD>technically bright but socially inept person
</DL>
Here is an example with multiple terms and descriptions:
<DL>
<DT>Center
<DT>Centre
<DD> A point equidistant from all points
on the surface of a sphere.
<DD> In some field sports, the player who
holds the middle position on the field, court,
or forward line.
</DL>
Another application of DL, for example, is for marking up dialogues,
with each DT naming a speaker, and each DD containing his or her
words.
10.3.1 Visual rendering of lists
Note. The following is an informative description of the behavior of
some current visual user agents when formatting lists. Style sheets
allow better control of list formatting (e.g., for numbering,
language-dependent conventions, indenting, etc.).
Visual user agents generally indent nested lists with respect to the
current level of nesting.
For both OL and UL, the type attribute specifies rendering options for
visual user agents.
For the UL element, possible values for the type attribute are disc,
square, and circle. The default value depends on the level of nesting
of the current list. These values are case-insensitive.
How each value is presented depends on the user agent. User agents
should attempt to present a "disc" as a small filled-in circle, a
"circle" as a small circle outline, and a "square" as a small square
outline.
A graphical user agent might render this as:
A possible rendering of a disc for the value "disc"
A possible rendering of a circle for the value "circle"
A possible rendering of a square for the value "square"
For the OL element, possible values for the type attribute are
summarized in the table below (they are case-sensitive):
Type Numbering style
1 arabic numbers 1, 2, 3, ...
a lower alpha a, b, c, ...
A upper alpha A, B, C, ...
i lower roman i, ii, iii, ...
I upper roman I, II, III, ...
Note that the type attribute is deprecated and list styles should be
handled through style sheets.
For example, using CSS, one may specify that the style of numbers for
list elements in a numbered list should be lowercase roman numerals.
In the excerpt below, every OL element belonging to the class
"withroman" will have roman numerals in front of its list items.
<STYLE type="text/css">
OL.withroman { list-style-type: lower-roman }
</STYLE>
<BODY>
<OL class="withroman">
<LI> Step one ...
<LI> Step two ...
</OL>
</BODY>
The rendering of a definition list also depends on the user agent. The
example:
<DL>
<DT>Dweeb
<DD>young excitable person who may mature
into a <EM>Nerd</EM> or <EM>Geek</EM>
<DT>Hacker
<DD>a clever programmer
<DT>Nerd
<DD>technically bright but socially inept person
</DL>
might be rendered as follows:
Dweeb
young excitable person who may mature into a Nerd or Geek
Hacker
a clever programmer
Nerd
technically bright but socially inept person
10.4 The DIR and MENU elements
DIR and MENU are deprecated.
See the Transitional DTD for the formal definition.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
The DIR element was designed to be used for creating multicolumn
directory lists. The MENU element was designed to be used for single
column menu lists. Both elements have the same structure as UL, just
different rendering. In practice, a user agent will render a DIR or
MENU list exactly as a UL list.
We strongly recommend using UL instead of these elements.
11 Tables
Contents
1. Introduction to tables
2. Elements for constructing tables
1. The TABLE element
o Table directionality
2. Table Captions: The CAPTION element
3. Row groups: the THEAD, TFOOT, and TBODY elements
4. Column groups: the COLGROUP and COL elements
o The COLGROUP element
o The COL element
o Calculating the number of columns in a table
o Calculating the width of columns
5. Table rows: The TR element
6. Table cells: The TH and TD elements
o Cells that span several rows or columns
3. Table formatting by visual user agents
1. Borders and rules
2. Horizontal and vertical alignment
o Inheritance of alignment specifications
3. Cell margins
4. Table rendering by non-visual user agents
1. Associating header information with data cells
2. Categorizing cells
3. Algorithm to find heading information
5. Sample table
11.1 Introduction to tables
The HTML table model allows authors to arrange data -- text,
preformatted text, images, links, forms, form fields, other tables,
etc. -- into rows and columns of cells.
Each table may have an associated caption (see the CAPTION element)
that provides a short description of the table's purpose. A longer
description may also be provided (via the summary attribute) for the
benefit of people using speech or Braille-based user agents.
Table rows may be grouped into a head, foot, and body sections, (via
the THEAD, TFOOT and TBODY elements, respectively). Row groups convey
additional structural information and may be rendered by user agents
in ways that emphasize this structure. User agents may exploit the
head/body/foot division to support scrolling of body sections
independently of the head and foot sections. When long tables are
printed, the head and foot information may be repeated on each page
that contains table data.
Authors may also group columns to provide additional structural
information that may be exploited by user agents. Furthermore, authors
may declare column properties at the start of a table definition (via
the COLGROUP and COL elements) in a way that enables user agents to
render the table incrementally rather than having to wait for all the
table data to arrive before rendering.
Table cells may either contain "header" information (see the TH
element) or "data" (see the TD element). Cells may span multiple rows
and columns. The HTML 4 table model allows authors to label each cell
so that non-visual user agents may more easily communicate heading
information about the cell to the user. Not only do these mechanisms
greatly assist users with visual disabilities, they make it possible
for multi-modal wireless browsers with limited display capabilities
(e.g., Web-enabled pagers and phones) to handle tables.
Tables should not be used purely as a means to layout document content
as this may present problems when rendering to non-visual media.
Additionally, when used with graphics, these tables may force users to
scroll horizontally to view a table designed on a system with a larger
display. To minimize these problems, authors should use style sheets
to control layout rather than tables.
Note. This specification includes more detailed information about
tables in sections on table design rationale and implementation
issues.
Here's a simple table that illustrates some of the features of the
HTML table model. The following table definition:
<TABLE border="1"
summary="This table gives some statistics about fruit
flies: average height and weight, and percentage
with red eyes (for both males and females).">
<CAPTION><EM>A test table with merged cells</EM></CAPTION>
<TR><TH rowspan="2"><TH colspan="2">Average
<TH rowspan="2">Red<BR>eyes
<TR><TH>height<TH>weight
<TR><TH>Males<TD>1.9<TD>0.003<TD>40%
<TR><TH>Females<TD>1.7<TD>0.002<TD>43%
</TABLE>
might be rendered something like this on a tty device:
A test table with merged cells
/-----------------------------------------\
| | Average | Red |
| |-------------------| eyes |
| | height | weight | |
|-----------------------------------------|
| Males | 1.9 | 0.003 | 40% |
|-----------------------------------------|
| Females | 1.7 | 0.002 | 43% |
\-----------------------------------------/
or like this by a graphical user agent:
A table with merged cells
11.2 Elements for constructing tables
11.2.1 The TABLE element
<!ELEMENT TABLE - -
(CAPTION?, (COL*|COLGROUP*), THEAD?, TFOOT?, TBODY+)>
<!ATTLIST TABLE -- table element --
%attrs; -- %coreattrs, %i18n, %events --
summary %Text; #IMPLIED -- purpose/structure for speech output--
width %Length; #IMPLIED -- table width --
border %Pixels; #IMPLIED -- controls frame width around table --
frame %TFrame; #IMPLIED -- which parts of frame to render --
rules %TRules; #IMPLIED -- rulings between rows and cols --
cellspacing %Length; #IMPLIED -- spacing between cells --
cellpadding %Length; #IMPLIED -- spacing within cells --
>
Start tag: required, End tag: required
Attribute definitions
summary = text [CS]
This attribute provides a summary of the table's purpose and
structure for user agents rendering to non-visual media such as
speech and Braille.
align = left|center|right [CI]
Deprecated. This attribute specifies the position of the table
with respect to the document. Permitted values:
+ left: The table is to the left of the document.
+ center: The table is to the center of the document.
+ right: The table is to the right of the document.
width = length [CN]
This attribute specifies the desired width of the entire table
and is intended for visual user agents. When the value is a
percentage value, the value is relative to the user agent's
available horizontal space. In the absence of any width
specification, table width is determined by the user agent.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
* bgcolor (background color)
* frame, rules, border (borders and rules)
* cellspacing, cellpadding (cell margins)
The TABLE element contains all other elements that specify caption,
rows, content, and formatting.
The following informative list describes what operations user agents
may carry out when rendering a table:
* Make the table summary available to the user. Authors should
provide a summary of a table's content and structure so that
people using non-visual user agents may better understand it.
* Render the caption, if one is defined.
* Render the table header, if one is specified. Render the table
footer, if one is specified. User agents must know where to render
the header and footer. For instance, if the output medium is
paged, user agents may put the header at the top of each page and
the footer at the bottom. Similarly, if the user agent provides a
mechanism to scroll the rows, the header may appear at the top of
the scrolled area and the footer at the bottom.
* Calculate the number of columns in the table. Note that the number
of rows in a table is equal to the number of TR elements contained
by the TABLE element.
* Group the columns according to any column group specifications.
* Render the cells, row by row and grouped in appropriate columns,
between the header and footer. Visual user agents should format
the table according to HTML attributes and style sheet
specification.
The HTML table model has been designed so that, with author
assistance, user agents may render tables incrementally (i.e., as
table rows arrive) rather than having to wait for all the data before
beginning to render.
In order for a user agent to format a table in one pass, authors must
tell the user agent:
* The number of columns in the table. Please consult the section on
calculating the number of columns in a table for details on how
to supply this information.
* The widths of these columns. Please consult the section on
calculating the width of columns for details on how to supply
this information.
More precisely, a user agent may render a table in a single pass when
the column widths are specified using a combination of COLGROUP and
COL elements. If any of the columns are specified in relative or
percentage terms (see the section on calculating the width of
columns), authors must also specify the width of the table itself.
Table directionality
The directionality of a table is either the inherited directionality
(the default is left-to-right) or that specified by the dir attribute
for the TABLE element.
For a left-to-right table, column zero is on the left side and row
zero is at the top. For a right-to-left table, column zero is on the
right side and row zero is at the top.
When a user agent allots extra cells to a row (see the section on
calculating the number of columns in a table), extra row cells are
added to the right of the table for left-to-right tables and to the
left side for right-to-left tables.
Note that TABLE is the only element on which dir reverses the visual
order of the columns; a single table row (TR) or a group of columns
(COLGROUP) cannot be independently reversed.
When set for the TABLE element, the dir attribute also affects the
direction of text within table cells (since the dir attribute is
inherited by block-level elements).
To specify a right-to-left table, set the dir attribute as follows:
<TABLE dir="RTL">
...the rest of the table...
</TABLE>
The direction of text in individual cells can be changed by setting
the dir attribute in an element that defines the cell. Please consult
the section on bidirectional text for more information on text
direction issues.
11.2.2 Table Captions: The CAPTION element
<!ELEMENT CAPTION - - (%inline;)* -- table caption -->
<!ATTLIST CAPTION
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: required
Attribute definitions
align = top|bottom|left|right [CI]
Deprecated. For visual user agents, this attribute specifies
the position of the caption with respect to the table. Possible
values:
+ top: The caption is at the top of the table. This is the
default value.
+ bottom: The caption is at the bottom of the table.
+ left: The caption is at the left of the table.
+ right: The caption is at the right of the table.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events )
When present, the CAPTION element's text should describe the nature of
the table. The CAPTION element is only permitted immediately after the
TABLE start tag. A TABLE element may only contain one CAPTION element.
Visual user agents allow sighted people to quickly grasp the structure
of the table from the headings as well as the caption. A consequence
of this is that captions will often be inadequate as a summary of the
purpose and structure of the table from the perspective of people
relying on non-visual user agents.
Authors should therefore take care to provide additional information
summarizing the purpose and structure of the table using the summary
attribute of the TABLE element. This is especially important for
tables without captions. Examples below illustrate the use of the
summary attribute.
Visual user agents should avoid clipping any part of the table
including the caption, unless a means is provided to access all parts,
e.g., by horizontal or vertical scrolling. We recommend that the
caption text be wrapped to the same width as the table. (See also the
section on recommended layout algorithms.)
11.2.3 Row groups: the THEAD, TFOOT, and TBODY elements
<!ELEMENT THEAD - O (TR)+ -- table header -->
<!ELEMENT TFOOT - O (TR)+ -- table footer -->
Start tag: required, End tag: optional
<!ELEMENT TBODY O O (TR)+ -- table body -->
Start tag: optional, End tag: optional
<!ATTLIST (THEAD|TBODY|TFOOT) -- table section --
%attrs; -- %coreattrs, %i18n, %events --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
>
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events )
* align, char, charoff, valign (cell alignment)
Table rows may be grouped into a table head, table foot, and one or
more table body sections, using the THEAD, TFOOT and TBODY elements,
respectively. This division enables user agents to support scrolling
of table bodies independently of the table head and foot. When long
tables are printed, the table head and foot information may be
repeated on each page that contains table data.
The table head and table foot should contain information about the
table's columns. The table body should contain rows of table data.
When present, each THEAD, TFOOT, and TBODY contains a row group. Each
row group must contain at least one row, defined by the TR element.
This example illustrates the order and structure of table heads, feet,
and bodies.
<TABLE>
<THEAD>
<TR> ...header information...
</THEAD>
<TFOOT>
<TR> ...footer information...
</TFOOT>
<TBODY>
<TR> ...first row of block one data...
<TR> ...second row of block one data...
</TBODY>
<TBODY>
<TR> ...first row of block two data...
<TR> ...second row of block two data...
<TR> ...third row of block two data...
</TBODY>
</TABLE>
TFOOT must appear before TBODY within a TABLE definition so that user
agents can render the foot before receiving all of the (potentially
numerous) rows of data. The following summarizes which tags are
required and which may be omitted:
* The TBODY start tag is always required except when the table
contains only one table body and no table head or foot sections.
The TBODY end tag may always be safely omitted.
* The start tags for THEAD and TFOOT are required when the table
head and foot sections are present respectively, but the
corresponding end tags may always be safely omitted.
Conforming user agent parsers must obey these rules for reasons of
backward compatibility.
The table of the previous example could be shortened by removing
certain end tags, as in:
<TABLE>
<THEAD>
<TR> ...header information...
<TFOOT>
<TR> ...footer information...
<TBODY>
<TR> ...first row of block one data...
<TR> ...second row of block one data...
<TBODY>
<TR> ...first row of block two data...
<TR> ...second row of block two data...
<TR> ...third row of block two data...
</TABLE>
The THEAD, TFOOT, and TBODY sections must contain the same number of
columns.
11.2.4 Column groups: the COLGROUP and COL elements
Column groups allow authors to create structural divisions within a
table. Authors may highlight this structure through style sheets or
HTML attributes (e.g., the rules attribute for the TABLE element). For
an example of the visual presentation of column groups, please consult
the sample table.
A table may either contain a single implicit column group (no COLGROUP
element delimits the columns) or any number of explicit column groups
(each delimited by an instance of the COLGROUP element).
The COL element allows authors to share attributes among several
columns without implying any structural grouping. The "span" of the
COL element is the number of columns that will share the element's
attributes.
The COLGROUP element
<!ELEMENT COLGROUP - O (COL)* -- table column group -->
<!ATTLIST COLGROUP
%attrs; -- %coreattrs, %i18n, %events --
span NUMBER 1 -- default number of columns in group --
width %MultiLength; #IMPLIED -- default width for enclosed COLs --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
>
Start tag: required, End tag: optional
Attribute definitions
span = number [CN]
This attribute, which must be an integer > 0, specifies the
number of columns in a column group. Values mean the following:
+ In the absence of a span attribute, each COLGROUP defines a
column group containing one column.
+ If the span attribute is set to N > 0, the current COLGROUP
element defines a column group containing N columns.
User agents must ignore this attribute if the COLGROUP element
contains one or more COL elements.
width = multi-length [CN]
This attribute specifies a default width for each column in the
current column group. In addition to the standard pixel,
percentage, and relative values, this attribute allows the
special form "0*" (zero asterisk) which means that the width of
the each column in the group should be the minimum width
necessary to hold the column's contents. This implies that a
column's entire contents must be known before its width may be
correctly computed. Authors should be aware that specifying
"0*" will prevent visual user agents from rendering a table
incrementally.
This attribute is overridden for any column in the column group
whose width is specified via a COL element.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events )
* align, char, charoff, valign (cell alignment)
The COLGROUP element creates an explicit column group. The number of
columns in the column group may be specified in two, mutually
exclusive ways:
1. The element's span attribute (default value 1) specifies the
number of columns in the group.
2. Each COL element in the COLGROUP represents one or more columns in
the group.
The advantage of using the span attribute is that authors may group
together information about column widths. Thus, if a table contains
forty columns, all of which have a width of 20 pixels, it is easier to
write:
<COLGROUP span="40" width="20">
</COLGROUP>
than:
<COLGROUP>
<COL width="20">
<COL width="20">
...a total of forty COL elements...
</COLGROUP>
When it is necessary to single out a column (e.g., for style
information, to specify width information, etc.) within a group,
authors must identify that column with a COL element. Thus, to apply
special style information to the last column of the previous table, we
single it out as follows:
<COLGROUP width="20">
<COL span="39">
<COL id="format-me-specially">
</COLGROUP>
The width attribute of the COLGROUP element is inherited by all 40
columns. The first COL element refers to the first 39 columns (doing
nothing special to them) and the second one assigns an id value to the
fortieth column so that style sheets may refer to it.
The table in the following example contains two column groups. The
first column group contains 10 columns and the second contains 5
columns. The default width for each column in the first column group
is 50 pixels. The width of each column in the second column group will
be the minimum required for that column.
<TABLE>
<COLGROUP span="10" width="50">
<COLGROUP span="5" width="0*">
<THEAD>
<TR><TD> ...
</TABLE>
The COL element
<!ELEMENT COL - O EMPTY -- table column -->
<!ATTLIST COL -- column groups and properties --
%attrs; -- %coreattrs, %i18n, %events --
span NUMBER 1 -- COL attributes affect N columns --
width %MultiLength; #IMPLIED -- column width specification --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
>
Start tag: required, End tag: forbidden
Attribute definitions
span = number [CN]
This attribute, whose value must be an integer > 0, specifies
the number of columns "spanned" by the COL element; the COL
element shares its attributes with all the columns it spans.
The default value for this attribute is 1 (i.e., the COL
element refers to a single column). If the span attribute is
set to N > 1, the current COL element shares its attributes
with the next N-1 columns.
width = multi-length [CN]
This attribute specifies a default width for each column
spanned by the current COL element. It has the same meaning as
the width attribute for the COLGROUP element and overrides it.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events )
* align, char, charoff, valign (cell alignment)
The COL element allows authors to group together attribute
specifications for table columns. The COL does not group columns
together structurally -- that is the role of the COLGROUP element. COL
elements are empty and serve only as a support for attributes. They
may appear inside or outside an explicit column group (i.e., COLGROUP
element).
The width attribute for COL refers to the width of each column in the
element's span.
Calculating the number of columns in a table
There are two ways to determine the number of columns in a table (in
order of precedence):
1. If the TABLE element contains any COLGROUP or COL elements, user
agents should calculate the number of columns by summing the
following:
+ For each COL element, take the value of its span attribute
(default value 1).
+ For each COLGROUP element containing at least one COL
element, ignore the span attribute for the COLGROUP element.
For each COL element, perform the calculation of step 1.
+ For each empty COLGROUP element, take the value of its span
attribute (default value 1).
2. Otherwise, if the TABLE element contains no COLGROUP or COL
elements, user agents should base the number of columns on what is
required by the rows. The number of columns is equal to the number
of columns required by the row with the most columns, including
cells that span multiple columns. For any row that has fewer than
this number of columns, the end of that row should be padded with
empty cells. The "end" of a row depends on the table
directionality.
It is an error if a table contains COLGROUP or COL elements and the
two calculations do not result in the same number of columns.
Once the user agent has calculated the number of columns in the table,
it may group them into column groups.
For example, for each of the following tables, the two column
calculation methods should result in three columns. The first three
tables may be rendered incrementally.
<TABLE>
<COLGROUP span="3"></COLGROUP>
<TR><TD> ...
...rows...
</TABLE>
<TABLE>
<COLGROUP>
<COL>
<COL span="2">
</COLGROUP>
<TR><TD> ...
...rows...
</TABLE>
<TABLE>
<COLGROUP>
<COL>
</COLGROUP>
<COLGROUP span="2">
<TR><TD> ...
...rows...
</TABLE>
<TABLE>
<TR>
<TD><TD><TD>
</TR>
</TABLE>
Calculating the width of columns
Authors may specify column widths in three ways:
Fixed
A fixed width specification is given in pixels (e.g.,
width="30"). A fixed-width specification enables incremental
rendering.
Percentage
A percentage specification (e.g., width="20%") is based on the
percentage of the horizontal space available to the table
(between the current left and right margins, including floats).
Note that this space does not depend on the table itself, and
thus percentage specifications enable incremental rendering.
Proportional
Proportional specifications (e.g., width="3*") refer to
portions of the horizontal space required by a table. If the
table width is given a fixed value via the width attribute of
the TABLE element, user agents may render the table
incrementally even with proportional columns.
However, if the table does not have a fixed width, user agents
must receive all table data before they can determine the
horizontal space required by the table. Only then may this
space be allotted to proportional columns.
If an author specifies no width information for a column, a user agent
may not be able to incrementally format the table since it must wait
for the entire column of data to arrive in order to allot an
appropriate width.
If column widths prove to be too narrow for the contents of a
particular table cell, user agents may choose to reflow the table.
The table in this example contains six columns. The first one does not
belong to an explicit column group. The next three belong to the first
explicit column group and the last two belong to the second explicit
column group. This table cannot be formatted incrementally since it
contains proportional column width specifications and no value for the
width attribute for the TABLE element.
Once the (visual) user agent has received the table's data: the
available horizontal space will be alloted by the user agent as
follows: First the user agent will allot 30 pixels to columns one and
two. Then, the minimal space required for the third column will be
reserved. The remaining horizontal space will be divided into six
equal portions (since 2* + 1* + 3* = 6 portions). Column four (2*)
will receive two of these portions, column five (1*) will receive one,
and column six (3*) will receive three.
<TABLE>
<COLGROUP>
<COL width="30">
<COLGROUP>
<COL width="30">
<COL width="0*">
<COL width="2*">
<COLGROUP align="center">
<COL width="1*">
<COL width="3*" align="char" char=":">
<THEAD>
<TR><TD> ...
...rows...
</TABLE>
We have set the value of the align attribute in the third column group
to "center". All cells in every column in this group will inherit this
value, but may override it. In fact, the final COL does just that, by
specifying that every cell in the column it governs will be aligned
along the ":" character.
In the following table, the column width specifications allow the user
agent to format the table incrementally:
<TABLE width="200">
<COLGROUP span="10" width="15">
<COLGROUP width="*">
<COL id="penultimate-column">
<COL id="last-column">
<THEAD>
<TR><TD> ...
...rows...
</TABLE>
The first ten columns will be 15 pixels wide each. The last two
columns will each receive half of the remaining 50 pixels. Note that
the COL elements appear only so that an id value may be specified for
the last two columns.
Note. Although the width attribute on the TABLE element is not
deprecated, authors are encouraged to use style sheets to specify
table widths.
11.2.5 Table rows: The TR element
<!ELEMENT TR - O (TH|TD)+ -- table row -->
<!ATTLIST TR -- table row --
%attrs; -- %coreattrs, %i18n, %events --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
>
Start tag: required, End tag: optional
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events )
* bgcolor (background color)
* align, char, charoff, valign (cell alignment)
The TR elements acts as a container for a row of table cells. The end
tag may be omitted.
This sample table contains three rows, each begun by the TR element:
<TABLE summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR> ...A header row...
<TR> ...First row of data...
<TR> ...Second row of data...
...the rest of the table...
</TABLE>
11.2.6 Table cells: The TH and TD elements
<!ELEMENT (TH|TD) - O (%flow;)* -- table header cell, table data cell-->
<!-- Scope is simpler than headers attribute for common tables -->
<!ENTITY % Scope "(row|col|rowgroup|colgroup)">
<!-- TH is for headers, TD for data, but for cells acting as both use TD -->
<!ATTLIST (TH|TD) -- header or data cell --
%attrs; -- %coreattrs, %i18n, %events --
abbr %Text; #IMPLIED -- abbreviation for header cell --
axis CDATA #IMPLIED -- comma-separated list of related heade
rs--
headers IDREFS #IMPLIED -- list of id's for header cells --
scope %Scope; #IMPLIED -- scope covered by header cells --
rowspan NUMBER 1 -- number of rows spanned by cell --
colspan NUMBER 1 -- number of cols spanned by cell --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
>
Start tag: required, End tag: optional
Attribute definitions
headers = idrefs [CS]
This attribute specifies the list of header cells that provide
header information for the current data cell. The value of this
attribute is a space-separated list of cell names; those cells
must be named by setting their id attribute. Authors generally
use the headers attribute to help non-visual user agents render
header information about data cells (e.g., header information
is spoken prior to the cell data), but the attribute may also
be used in conjunction with style sheets. See also the scope
attribute.
scope = scope-name [CI]
This attribute specifies the set of data cells for which the
current header cell provides header information. This attribute
may be used in place of the headers attribute, particularly for
simple tables. When specified, this attribute must have one of
the following values:
+ row: The current cell provides header information for the
rest of the row that contains it (see also the section on
table directionality).
+ col: The current cell provides header information for the
rest of the column that contains it.
+ rowgroup: The header cell provides header information for the
rest of the row group that contains it.
+ colgroup: The header cell provides header information for the
rest of the column group that contains it.
abbr = text [CS]
This attribute should be used to provide an abbreviated form of
the cell's content, and may be rendered by user agents when
appropriate in place of the cell's content. Abbreviated names
should be short since user agents may render them repeatedly.
For instance, speech synthesizers may render the abbreviated
headers relating to a particular cell before rendering that
cell's content.
axis = cdata [CI]
This attribute may be used to place a cell into conceptual
categories that can be considered to form axes in an
n-dimensional space. User agents may give users access to these
categories (e.g., the user may query the user agent for all
cells that belong to certain categories, the user agent may
present a table in the form of a table of contents, etc.).
Please consult the section on categorizing cells for more
information. The value of this attribute is a comma-separated
list of category names.
rowspan = number [CN]
This attribute specifies the number of rows spanned by the
current cell. The default value of this attribute is one ("1").
The value zero ("0") means that the cell spans all rows from
the current row to the last row of the table section (THEAD,
TBODY, or TFOOT) in which the cell is defined.
colspan = number [CN]
This attribute specifies the number of columns spanned by the
current cell. The default value of this attribute is one ("1").
The value zero ("0") means that the cell spans all columns from
the current column to the last column of the column group
(COLGROUP) in which the cell is defined.
nowrap [CI]
Deprecated. When present, this boolean attribute tells visual
user agents to disable automatic text wrapping for this cell.
Style sheets should be used instead of this attribute to
achieve wrapping effects. Note. if used carelessly, this
attribute may result in excessively wide cells.
width = length [CN]
Deprecated. This attribute supplies user agents with a
recommended cell width.
height = length [CN]
Deprecated. This attribute supplies user agents with a
recommended cell height.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events )
* bgcolor (background color)
* align, char, charoff, valign (cell alignment)
Table cells may contain two types of information: header information
and data. This distinction enables user agents to render header and
data cells distinctly, even in the absence of style sheets. For
example, visual user agents may present header cell text with a bold
font. Speech synthesizers may render header information with a
distinct voice inflection.
The TH element defines a cell that contains header information. User
agents have two pieces of header information available: the contents
of the TH element and the value of the abbr attribute. User agents
must render either the contents of the cell or the value of the abbr
attribute. For visual media, the latter may be appropriate when there
is insufficient space to render the full contents of the cell. For
non-visual media abbr may be used as an abbreviation for table headers
when these are rendered along with the contents of the cells to which
they apply.
The headers and scope attributes also allow authors to help non-visual
user agents process header information. Please consult the section on
labeling cells for non-visual user agents for information and
examples.
The TD element defines a cell that contains data.
Cells may be empty (i.e., contain no data).
For example, the following table contains four columns of data, each
headed by a column description.
<TABLE summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
<TH>Name</TH>
<TH>Cups</TH>
<TH>Type of Coffee</TH>
<TH>Sugar?</TH>
<TR>
<TD>T. Sexton</TD>
<TD>10</TD>
<TD>Espresso</TD>
<TD>No</TD>
<TR>
<TD>J. Dinnen</TD>
<TD>5</TD>
<TD>Decaf</TD>
<TD>Yes</TD>
</TABLE>
A user agent rendering to a tty device might display this as follows:
Name Cups Type of Coffee Sugar?
T. Sexton 10 Espresso No
J. Dinnen 5 Decaf Yes
Cells that span several rows or columns
Cells may span several rows or columns. The number of rows or columns
spanned by a cell is set by the rowspan and colspan attributes for the
TH and TD elements.
In this table definition, we specify that the cell in row four, column
two should span a total of three columns, including the current
column.
<TABLE border="1">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR><TH>Name<TH>Cups<TH>Type of Coffee<TH>Sugar?
<TR><TD>T. Sexton<TD>10<TD>Espresso<TD>No
<TR><TD>J. Dinnen<TD>5<TD>Decaf<TD>Yes
<TR><TD>A. Soria<TD colspan="3"><em>Not available</em>
</TABLE>
This table might be rendered on a tty device by a visual user agent as
follows:
Cups of coffee consumed by each senator
--------------------------------------
| Name |Cups|Type of Coffee|Sugar?|
--------------------------------------
|T. Sexton|10 |Espresso |No |
--------------------------------------
|J. Dinnen|5 |Decaf |Yes |
--------------------------------------
|A. Soria |Not available |
--------------------------------------
The next example illustrates (with the help of table borders) how cell
definitions that span more than one row or column affect the
definition of later cells. Consider the following table definition:
<TABLE border="1">
<TR><TD>1 <TD rowspan="2">2 <TD>3
<TR><TD>4 <TD>6
<TR><TD>7 <TD>8 <TD>9
</TABLE>
As cell "2" spans the first and second rows, the definition of the
second row will take it into account. Thus, the second TD in row two
actually defines the row's third cell. Visually, the table might be
rendered to a tty device as:
-------------
| 1 | 2 | 3 |
----| |----
| 4 | | 6 |
----|---|----
| 7 | 8 | 9 |
-------------
while a graphical user agent might render this as:
Image of a table with rowspan=2
Note that if the TD defining cell "6" had been omitted, an extra empty
cell would have been added by the user agent to complete the row.
Similarly, in the following table definition:
<TABLE border="1">
<TR><TD>1 <TD>2 <TD>3
<TR><TD colspan="2">4 <TD>6
<TR><TD>7 <TD>8 <TD>9
</TABLE>
cell "4" spans two columns, so the second TD in the row actually
defines the third cell ("6"):
-------------
| 1 | 2 | 3 |
--------|----
| 4 | 6 |
--------|----
| 7 | 8 | 9 |
-------------
A graphical user agent might render this as:
Image of a table with colspan=2
Defining overlapping cells is an error. User agents may vary in how
they handle this error (e.g., rendering may vary).
The following illegal example illustrates how one might create
overlapping cells. In this table, cell "5" spans two rows and cell "7"
spans two columns, so there is overlap in the cell between "7" and
"9":
<TABLE border="1">
<TR><TD>1 <TD>2 <TD>3
<TR><TD>4 <TD rowspan="2">5 <TD>6
<TR><TD colspan="2">7 <TD>9
</TABLE>
11.3 Table formatting by visual user agents
Note. The following sections describe the HTML table attributes that
concern visual formatting. When this specification was first published
in 1997, [CSS1] did not offer mechanisms to control all aspects of
visual table formatting. Since then, [CSS2] has added properties to
allow visual formatting of tables.
HTML 4 includes mechanisms to control:
* border styles
* horizontal and vertical alignment of cell contents
* and cell margins
11.3.1 Borders and rules
The following attributes affect a table's external frame and internal
rules.
Attribute definitions
frame = void|above|below|hsides|lhs|rhs|vsides|box|border [CI]
This attribute specifies which sides of the frame surrounding a
table will be visible. Possible values:
+ void: No sides. This is the default value.
+ above: The top side only.
+ below: The bottom side only.
+ hsides: The top and bottom sides only.
+ vsides: The right and left sides only.
+ lhs: The left-hand side only.
+ rhs: The right-hand side only.
+ box: All four sides.
+ border: All four sides.
rules = none|groups|rows|cols|all [CI]
This attribute specifies which rules will appear between cells
within a table. The rendering of rules is user agent dependent.
Possible values:
+ none: No rules. This is the default value.
+ groups: Rules will appear between row groups (see THEAD,
TFOOT, and TBODY) and column groups (see COLGROUP and COL)
only.
+ rows: Rules will appear between rows only.
+ cols: Rules will appear between columns only.
+ all: Rules will appear between all rows and columns.
border = pixels [CN]
This attributes specifies the width (in pixels only) of the
frame around a table (see the Note below for more information
about this attribute).
To help distinguish the cells of a table, we can set the border
attribute of the TABLE element. Consider a previous example:
<TABLE border="1"
summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
<TH>Name</TH>
<TH>Cups</TH>
<TH>Type of Coffee</TH>
<TH>Sugar?</TH>
<TR>
<TD>T. Sexton</TD>
<TD>10</TD>
<TD>Espresso</TD>
<TD>No</TD>
<TR>
<TD>J. Dinnen</TD>
<TD>5</TD>
<TD>Decaf</TD>
<TD>Yes</TD>
</TABLE>
In the following example, the user agent should show borders five
pixels thick on the left-hand and right-hand sides of the table, with
rules drawn between each column.
<TABLE border="5" frame="vsides" rules="cols">
<TR> <TD>1 <TD>2 <TD>3
<TR> <TD>4 <TD>5 <TD>6
<TR> <TD>7 <TD>8 <TD>9
</TABLE>
The following settings should be observed by user agents for backwards
compatibility.
* Setting border="0" implies frame="void" and, unless otherwise
specified, rules="none".
* Other values of border imply frame="border" and, unless otherwise
specified, rules="all".
* The value "border" in the start tag of the TABLE element should be
interpreted as the value of the frame attribute. It implies
rules="all" and some default (non-zero) value for the border
attribute.
For example, the following definitions are equivalent:
<TABLE border="2">
<TABLE border="2" frame="border" rules="all">
as are the following:
<TABLE border>
<TABLE frame="border" rules="all">
Note. The border attribute also defines the border behavior for the
OBJECT and IMG elements, but takes different values for those
elements.
11.3.2 Horizontal and vertical alignment
The following attributes may be set for different table elements (see
their definitions).
<!-- horizontal alignment attributes for cell contents -->
<!ENTITY % cellhalign
"align (left|center|right|justify|char) #IMPLIED
char %Character; #IMPLIED -- alignment char, e.g. char=':' --
charoff %Length; #IMPLIED -- offset for alignment char --"
>
<!-- vertical alignment attributes for cell contents -->
<!ENTITY % cellvalign
"valign (top|middle|bottom|baseline) #IMPLIED"
>
Attribute definitions
align = left|center|right|justify|char [CI]
This attribute specifies the alignment of data and the
justification of text in a cell. Possible values:
+ left: Left-flush data/Left-justify text. This is the default
value for table data.
+ center: Center data/Center-justify text. This is the default
value for table headers.
+ right: Right-flush data/Right-justify text.
+ justify: Double-justify text.
+ char: Align text around a specific character. If a user agent
doesn't support character alignment, behavior in the presence
of this value is unspecified.
valign = top|middle|bottom|baseline [CI]
This attribute specifies the vertical position of data within a
cell. Possible values:
+ top: Cell data is flush with the top of the cell.
+ middle: Cell data is centered vertically within the cell.
This is the default value.
+ bottom: Cell data is flush with the bottom of the cell.
+ baseline: All cells in the same row as a cell whose valign
attribute has this value should have their textual data
positioned so that the first text line occurs on a baseline
common to all cells in the row. This constraint does not
apply to subsequent text lines in these cells.
char = character [CN]
This attribute specifies a single character within a text
fragment to act as an axis for alignment. The default value for
this attribute is the decimal point character for the current
language as set by the lang attribute (e.g., the period (".")
in English and the comma (",") in French). User agents are not
required to support this attribute.
charoff = length [CN]
When present, this attribute specifies the offset to the first
occurrence of the alignment character on each line. If a line
doesn't include the alignment character, it should be
horizontally shifted to end at the alignment position.
When charoff is used to set the offset of an alignment
character, the direction of offset is determined by the current
text direction (set by the dir attribute). In left-to-right
texts (the default), offset is from the left margin. In
right-to-left texts, offset is from the right margin. User
agents are not required to support this attribute.
The table in this example aligns a row of currency values along a
decimal point. We set the alignment character to "." explicitly.
<TABLE border="1">
<COLGROUP>
<COL><COL align="char" char=".">
<THEAD>
<TR><TH>Vegetable <TH>Cost per kilo
<TBODY>
<TR><TD>Lettuce <TD>$1
<TR><TD>Silver carrots <TD>$10.50
<TR><TD>Golden turnips <TD>$100.30
</TABLE>
The formatted table may resemble the following:
------------------------------
| Vegetable |Cost per kilo|
|--------------|-------------|
|Lettuce | $1 |
|--------------|-------------|
|Silver carrots| $10.50|
|--------------|-------------|
|Golden turnips| $100.30|
------------------------------
When the contents of a cell contain more than one instance of the
alignment character specified by char and the contents wrap, user
agent behavior is undefined. Authors should therefore be attentive in
their use of char.
Note. Visual user agents typically render TH elements vertically and
horizontally centered within the cell and with a bold font weight.
Inheritance of alignment specifications
The alignment of cell contents can be specified on a cell by cell
basis, or inherited from enclosing elements, such as the row, column
or the table itself.
The order of precedence (from highest to lowest) for the attributes
align, char, and charoff is the following:
1. An alignment attribute set on an element within a cell's data
(e.g., P).
2. An alignment attribute set on a cell (TH and TD).
3. An alignment attribute set on a column grouping element (COL and
COLGROUP). When a cell is part of a multi-column span, the
alignment property is inherited from the cell definition at the
beginning of the span.
4. An alignment attribute set on a row or row grouping element (TR,
THEAD, TFOOT, and TBODY). When a cell is part of a multi-row
span, the alignment property is inherited from the cell definition
at the beginning of the span.
5. An alignment attribute set on the table (TABLE).
6. The default alignment value.
The order of precedence (from highest to lowest) for the attribute
valign (as well as the other inherited attributes lang, dir, and
style) is the following:
1. An attribute set on an element within a cell's data (e.g., P).
2. An attribute set on a cell (TH and TD).
3. An attribute set on a row or row grouping element (TR, THEAD,
TFOOT, and TBODY). When a cell is part of a multi-row span, the
attribute value is inherited from the cell definition at the
beginning of the span.
4. An attribute set on a column grouping element (COL and COLGROUP).
When a cell is part of a multi-column span, the attribute value is
inherited from the cell definition at the beginning of the span.
5. An attribute set on the table (TABLE).
6. The default attribute value.
Furthermore, when rendering cells, horizontal alignment is determined
by columns in preference to rows, while for vertical alignment, rows
are given preference over columns.
The default alignment for cells depends on the user agent. However,
user agents should substitute the default attribute for the current
directionality (i.e., not just "left" in all cases).
User agents that do not support the "justify" value of the align
attribute should use the value of the inherited directionality in its
place.
Note. Note that a cell may inherit an attribute not from its parent
but from the first cell in a span. This is an exception to the general
attribute inheritance rules.
11.3.3 Cell margins
Attribute definitions
cellspacing = length [CN]
This attribute specifies how much space the user agent should
leave between the left side of the table and the left-hand side
of the leftmost column, the top of the table and the top side
of the topmost row, and so on for the right and bottom of the
table. The attribute also specifies the amount of space to
leave between cells.
cellpadding = length [CN]
This attribute specifies the amount of space between the border
of the cell and its contents. If the value of this attribute is
a pixel length, all four margins should be this distance from
the contents. If the value of the attribute is a percentage
length, the top and bottom margins should be equally separated
from the content based on a percentage of the available
vertical space, and the left and right margins should be
equally separated from the content based on a percentage of the
available horizontal space.
These two attributes control spacing between and within cells. The
following illustration explains how they relate:
Image illustrating how cellspacing and cellpadding attributes relate.
In the following example, the cellspacing attribute specifies that
cells should be separated from each other and from the table frame by
twenty pixels. The cellpadding attribute specifies that the top margin
of the cell and the bottom margin of the cell will each be separated
from the cell's contents by 10% of the available vertical space (the
total being 20%). Similarly, the left margin of the cell and the right
margin of the cell will each be separated from the cell's contents by
10% of the available horizontal space (the total being 20%).
<TABLE cellspacing="20" cellpadding="20%">
<TR> <TD>Data1 <TD>Data2 <TD>Data3
</TABLE>
If a table or given column has a fixed width, cellspacing and
cellpadding may demand more space than assigned. User agents may give
these attributes precedence over the width attribute when a conflict
occurs, but are not required to.
11.4 Table rendering by non-visual user agents
11.4.1 Associating header information with data cells
Non-visual user agents such as speech synthesizers and Braille-based
devices may use the following TD and TH element attributes to render
table cells more intuitively:
* For a given data cell, the headers attribute lists which cells
provide pertinent header information. For this purpose, each
header cell must be named using the id attribute. Note that it's
not always possible to make a clean division of cells into headers
or data. You should use the TD element for such cells together
with the id or scope attributes as appropriate.
* For a given header cell, the scope attribute tells the user agent
the data cells for which this header provides information. Authors
may choose to use this attribute instead of headers according to
which is more convenient; the two attributes fulfill the same
function. The headers attribute is generally needed when headers
are placed in irregular positions with respect to the data they
apply to.
* The abbr attribute specifies an abbreviated header for header
cells so that user agents may render header information more
rapidly.
In the following example, we assign header information to cells by
setting the headers attribute. Each cell in the same column refers to
the same header cell (via the id attribute).
<TABLE border="1"
summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
<TH id="t1">Name</TH>
<TH id="t2">Cups</TH>
<TH id="t3" abbr="Type">Type of Coffee</TH>
<TH id="t4">Sugar?</TH>
<TR>
<TD headers="t1">T. Sexton</TD>
<TD headers="t2">10</TD>
<TD headers="t3">Espresso</TD>
<TD headers="t4">No</TD>
<TR>
<TD headers="t1">J. Dinnen</TD>
<TD headers="t2">5</TD>
<TD headers="t3">Decaf</TD>
<TD headers="t4">Yes</TD>
</TABLE>
A speech synthesizer might render this table as follows:
Caption: Cups of coffee consumed by each senator
Summary: This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.
Name: T. Sexton, Cups: 10, Type: Espresso, Sugar: No
Name: J. Dinnen, Cups: 5, Type: Decaf, Sugar: Yes
Note how the header "Type of Coffee" is abbreviated to "Type" using
the abbr attribute.
Here is the same example substituting the scope attribute for the
headers attribute. Note the value "col" for the scope attribute,
meaning "all cells in the current column":
<TABLE border="1"
summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
<TH scope="col">Name</TH>
<TH scope="col">Cups</TH>
<TH scope="col" abbr="Type">Type of Coffee</TH>
<TH scope="col">Sugar?</TH>
<TR>
<TD>T. Sexton</TD>
<TD>10</TD>
<TD>Espresso</TD>
<TD>No</TD>
<TR>
<TD>J. Dinnen</TD>
<TD>5</TD>
<TD>Decaf</TD>
<TD>Yes</TD>
</TABLE>
Here's a somewhat more complex example illustrating other values for
the scope attribute:
<TABLE border="1" cellpadding="5" cellspacing="2"
summary="History courses offered in the community of
Bath arranged by course name, tutor, summary,
code, and fee">
<TR>
<TH colspan="5" scope="colgroup">Community Courses -- Bath Autumn 1997</TH>
</TR>
<TR>
<TH scope="col" abbr="Name">Course Name</TH>
<TH scope="col" abbr="Tutor">Course Tutor</TH>
<TH scope="col">Summary</TH>
<TH scope="col">Code</TH>
<TH scope="col">Fee</TH>
</TR>
<TR>
<TD scope="row">After the Civil War</TD>
<TD>Dr. John Wroughton</TD>
<TD>
The course will examine the turbulent years in England
after 1646. <EM>6 weekly meetings starting Monday 13th
October.</EM>
</TD>
<TD>H27</TD>
<TD>£32</TD>
</TR>
<TR>
<TD scope="row">An Introduction to Anglo-Saxon England</TD>
<TD>Mark Cottle</TD>
<TD>
One day course introducing the early medieval
period reconstruction the Anglo-Saxons and
their society. <EM>Saturday 18th October.</EM>
</TD>
<TD>H28</TD>
<TD>£18</TD>
</TR>
<TR>
<TD scope="row">The Glory that was Greece</TD>
<TD>Valerie Lorenz</TD>
<TD>
Birthplace of democracy, philosophy, heartland of theater, home of
argument. The Romans may have done it but the Greeks did it
first. <EM>Saturday day school 25th October 1997</EM>
</TD>
<TD>H30</TD>
<TD>£18</TD>
</TR>
</TABLE>
A graphical user agent might render this as:
A table with merged cells
Note the use of the scope attribute with the "row" value. Although the
first cell in each row contains data, not header information, the
scope attribute makes the data cell behave like a row header cell.
This allows speech synthesizers to provide the relevant course name
upon request or to state it immediately before each cell's content.
11.4.2 Categorizing cells
Users browsing a table with a speech-based user agent may wish to hear
an explanation of a cell's contents in addition to the contents
themselves. One way the user might provide an explanation is by
speaking associated header information before speaking the data cell's
contents (see the section on associating header information with data
cells).
Users may also want information about more than one cell, in which
case header information provided at the cell level (by headers, scope,
and abbr) may not provide adequate context. Consider the following
table, which classifies expenses for meals, hotels, and transport in
two locations (San Jose and Seattle) over several days:
Image of a table listing travel expenses at two locations: San Jose
and Seattle, by date, and category (meals, hotels, and transport),
shown with subtitles
Users might want to extract information from the table in the form of
queries:
* "What did I spend for all my meals?"
* "What did I spend for meals on 25 August?"
* "What did I spend for all expenses in San Jose?"
Each query involves a computation by the user agent that may involve
zero or more cells. In order to determine, for example, the costs of
meals on 25 August, the user agent must know which table cells refer
to "Meals" (all of them) and which refer to "Dates" (specifically, 25
August), and find the intersection of the two sets.
To accommodate this type of query, the HTML 4 table model allows
authors to place cell headers and data into categories. For example,
for the travel expense table, an author could group the header cells
"San Jose" and "Seattle" into the category "Location", the headers
"Meals", "Hotels", and "Transport" in the category "Expenses", and the
four days into the category "Date". The previous three questions would
then have the following meanings:
* "What did I spend for all my meals?" means "What are all the data
cells in the "Expenses=Meals" category?
* "What did I spend for meals on 25 August?" means "What are all the
data cells in the "Expenses=Meals" and "Date=Aug-25-1997"
categories?
* "What did I spend for all expenses in San Jose?" means "What are
all the data cells in the "Expenses=Meals, Hotels, Transport" and
"Location=San Jose" categories?
Authors categorize a header or data cell by setting the axis attribute
for the cell. For instance, in the travel expense table, the cell
containing the information "San Jose" could be placed in the
"Location" category as follows:
<TH id="a6" axis="location">San Jose</TH>
Any cell containing information related to "San Jose" should refer to
this header cell via either the headers or the scope attribute. Thus,
meal expenses for 25-Aug-1997 should be marked up to refer to id
attribute (whose value here is "a6") of the "San Jose" header cell:
<TD headers="a6">37.74</TD>
Each headers attribute provides a list of id references. Authors may
thus categorize a given cell in any number of ways (or, along any
number of "headers", hence the name).
Below we mark up the travel expense table with category information:
<TABLE border="1"
summary="This table summarizes travel expenses
incurred during August trips to
San Jose and Seattle">
<CAPTION>
Travel Expense Report
</CAPTION>
<TR>
<TH></TH>
<TH id="a2" axis="expenses">Meals</TH>
<TH id="a3" axis="expenses">Hotels</TH>
<TH id="a4" axis="expenses">Transport</TH>
<TD>subtotals</TD>
</TR>
<TR>
<TH id="a6" axis="location">San Jose</TH>
<TH></TH>
<TH></TH>
<TH></TH>
<TD></TD>
</TR>
<TR>
<TD id="a7" axis="date">25-Aug-97</TD>
<TD headers="a6 a7 a2">37.74</TD>
<TD headers="a6 a7 a3">112.00</TD>
<TD headers="a6 a7 a4">45.00</TD>
<TD></TD>
</TR>
<TR>
<TD id="a8" axis="date">26-Aug-97</TD>
<TD headers="a6 a8 a2">27.28</TD>
<TD headers="a6 a8 a3">112.00</TD>
<TD headers="a6 a8 a4">45.00</TD>
<TD></TD>
</TR>
<TR>
<TD>subtotals</TD>
<TD>65.02</TD>
<TD>224.00</TD>
<TD>90.00</TD>
<TD>379.02</TD>
</TR>
<TR>
<TH id="a10" axis="location">Seattle</TH>
<TH></TH>
<TH></TH>
<TH></TH>
<TD></TD>
</TR>
<TR>
<TD id="a11" axis="date">27-Aug-97</TD>
<TD headers="a10 a11 a2">96.25</TD>
<TD headers="a10 a11 a3">109.00</TD>
<TD headers="a10 a11 a4">36.00</TD>
<TD></TD>
</TR>
<TR>
<TD id="a12" axis="date">28-Aug-97</TD>
<TD headers="a10 a12 a2">35.00</TD>
<TD headers="a10 a12 a3">109.00</TD>
<TD headers="a10 a12 a4">36.00</TD>
<TD></TD>
</TR>
<TR>
<TD>subtotals</TD>
<TD>131.25</TD>
<TD>218.00</TD>
<TD>72.00</TD>
<TD>421.25</TD>
</TR>
<TR>
<TH>Totals</TH>
<TD>196.27</TD>
<TD>442.00</TD>
<TD>162.00</TD>
<TD>800.27</TD>
</TR>
</TABLE>
Note that marking up the table this way also allows user agents to
avoid confusing the user with unwanted information. For instance, if a
speech synthesizer were to speak all of the figures in the "Meals"
column of this table in response to the query "What were all my meal
expenses?", a user would not be able to distinguish a day's expenses
from subtotals or totals. By carefully categorizing cell data, authors
allow user agents to make important semantic distinctions when
rendering.
Of course, there is no limit to how authors may categorize information
in a table. In the travel expense table, for example, we could add the
additional categories "subtotals" and "totals".
This specification does not require user agents to handle information
provided by the axis attribute, nor does it make any recommendations
about how user agents may present axis information to users or how
users may query the user agent about this information.
However, user agents, particularly speech synthesizers, may want to
factor out information common to several cells that are the result of
a query. For instance, if the user asks "What did I spend for meals in
San Jose?", the user agent would first determine the cells in question
(25-Aug-1997: 37.74, 26-Aug-1997:27.28), then render this information.
A user agent speaking this information might read it:
Location: San Jose. Date: 25-Aug-1997. Expenses, Meals: 37.74
Location: San Jose. Date: 26-Aug-1997. Expenses, Meals: 27.28
or, more compactly:
San Jose, 25-Aug-1997, Meals: 37.74
San Jose, 26-Aug-1997, Meals: 27.28
An even more economical rendering would factor the common information
and reorder it:
San Jose, Meals, 25-Aug-1997: 37.74
26-Aug-1997: 27.28
User agents that support this type of rendering should allow user
agents a means to customize rendering (e.g., through style sheets).
11.4.3 Algorithm to find heading information
In the absence of header information from either the scope or headers
attribute, user agents may construct header information according to
the following algorithm. The goal of the algorithm is to find an
ordered list of headers. (In the following description of the
algorithm the table directionality is assumed to be left-to-right.)
* First, search left from the cell's position to find row header
cells. Then search upwards to find column header cells. The search
in a given direction stops when the edge of the table is reached
or when a data cell is found after a header cell.
* Row headers are inserted into the list in the order they appear in
the table. For left-to-right tables, headers are inserted from
left to right.
* Column headers are inserted after row headers, in the order they
appear in the table, from top to bottom.
* If a header cell has the headers attribute set, then the headers
referenced by this attribute are inserted into the list and the
search stops for the current direction.
* TD cells that set the axis attribute are also treated as header
cells.
11.5 Sample table
This sample illustrates grouped rows and columns. The example is
adapted from "Developing International Software", by Nadine Kano.
In "ascii art", the following table:
<TABLE border="2" frame="hsides" rules="groups"
summary="Code page support in different versions
of MS Windows.">
<CAPTION>CODE-PAGE SUPPORT IN MICROSOFT WINDOWS</CAPTION>
<COLGROUP align="center">
<COLGROUP align="left">
<COLGROUP align="center" span="2">
<COLGROUP align="center" span="3">
<THEAD valign="top">
<TR>
<TH>Code-Page<BR>ID
<TH>Name
<TH>ACP
<TH>OEMCP
<TH>Windows<BR>NT 3.1
<TH>Windows<BR>NT 3.51
<TH>Windows<BR>95
<TBODY>
<TR><TD>1200<TD>Unicode (BMP of ISO/IEC-10646)<TD><TD><TD>X<TD>X<TD>*
<TR><TD>1250<TD>Windows 3.1 Eastern European<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1251<TD>Windows 3.1 Cyrillic<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1252<TD>Windows 3.1 US (ANSI)<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1253<TD>Windows 3.1 Greek<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1254<TD>Windows 3.1 Turkish<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1255<TD>Hebrew<TD>X<TD><TD><TD><TD>X
<TR><TD>1256<TD>Arabic<TD>X<TD><TD><TD><TD>X
<TR><TD>1257<TD>Baltic<TD>X<TD><TD><TD><TD>X
<TR><TD>1361<TD>Korean (Johab)<TD>X<TD><TD><TD>**<TD>X
<TBODY>
<TR><TD>437<TD>MS-DOS United States<TD><TD>X<TD>X<TD>X<TD>X
<TR><TD>708<TD>Arabic (ASMO 708)<TD><TD>X<TD><TD><TD>X
<TR><TD>709<TD>Arabic (ASMO 449+, BCON V4)<TD><TD>X<TD><TD><TD>X
<TR><TD>710<TD>Arabic (Transparent Arabic)<TD><TD>X<TD><TD><TD>X
<TR><TD>720<TD>Arabic (Transparent ASMO)<TD><TD>X<TD><TD><TD>X
</TABLE>
would be rendered something like this:
CODE-PAGE SUPPORT IN MICROSOFT WINDOWS
===============================================================================
Code-Page | Name | ACP OEMCP | Windows Windows Windows
ID | | | NT 3.1 NT 3.51 95
-------------------------------------------------------------------------------
1200 | Unicode (BMP of ISO 10646) | | X X *
1250 | Windows 3.1 Eastern European | X | X X X
1251 | Windows 3.1 Cyrillic | X | X X X
1252 | Windows 3.1 US (ANSI) | X | X X X
1253 | Windows 3.1 Greek | X | X X X
1254 | Windows 3.1 Turkish | X | X X X
1255 | Hebrew | X | X
1256 | Arabic | X | X
1257 | Baltic | X | X
1361 | Korean (Johab) | X | ** X
-------------------------------------------------------------------------------
437 | MS-DOS United States | X | X X X
708 | Arabic (ASMO 708) | X | X
709 | Arabic (ASMO 449+, BCON V4) | X | X
710 | Arabic (Transparent Arabic) | X | X
720 | Arabic (Transparent ASMO) | X | X
===============================================================================
A graphical user agent might render this as:
A table with grouped rows and columns
This example illustrates how COLGROUP can be used to group columns and
set the default column alignment. Similarly, TBODY is used to group
rows. The frame and rules attributes tell the user agent which borders
and rules to render.
12 Links
Contents
1. Introduction to links and anchors
1. Visiting a linked resource
2. Other link relationships
3. Specifying anchors and links
4. Link titles
5. Internationalization and links
2. The A element
1. Syntax of anchor names
2. Nested links are illegal
3. Anchors with the id attribute
4. Unavailable and unidentifiable resources
3. Document relationships: the LINK element
1. Forward and reverse links
2. Links and external style sheets
3. Links and search engines
4. Path information: the BASE element
1. Resolving relative URIs
12.1 Introduction to links and anchors
HTML offers many of the conventional publishing idioms for rich text
and structured documents, but what separates it from most other markup
languages is its features for hypertext and interactive documents.
This section introduces the link (or hyperlink, or Web link), the
basic hypertext construct. A link is a connection from one Web
resource to another. Although a simple concept, the link has been one
of the primary forces driving the success of the Web.
A link has two ends -- called anchors -- and a direction. The link
starts at the "source" anchor and points to the "destination" anchor,
which may be any Web resource (e.g., an image, a video clip, a sound
bite, a program, an HTML document, an element within an HTML document,
etc.).
12.1.1 Visiting a linked resource
The default behavior associated with a link is the retrieval of
another Web resource. This behavior is commonly and implicitly
obtained by selecting the link (e.g., by clicking, through keyboard
input, etc.).
The following HTML excerpt contains two links, one whose destination
anchor is an HTML document named "chapter2.html" and the other whose
destination anchor is a GIF image in the file "forest.gif":
<BODY>
...some text...
<P>You'll find a lot more in <A href="chapter2.html">chapter two</A>.
See also this <A href="../images/forest.gif">map of the enchanted forest.</A>
</BODY>
By activating these links (by clicking with the mouse, through
keyboard input, voice commands, etc.), users may visit these
resources. Note that the href attribute in each source anchor
specifies the address of the destination anchor with a URI.
The destination anchor of a link may be an element within an HTML
document. The destination anchor must be given an anchor name and any
URI addressing this anchor must include the name as its fragment
identifier.
Destination anchors in HTML documents may be specified either by the A
element (naming it with the name attribute), or by any other element
(naming with the id attribute).
Thus, for example, an author might create a table of contents whose
entries link to header elements H2, H3, etc., in the same document.
Using the A element to create destination anchors, we would write:
<H1>Table of Contents</H1>
<P><A href="#section1">Introduction</A><BR>
<A href="#section2">Some background</A><BR>
<A href="#section2.1">On a more personal note</A><BR>
...the rest of the table of contents...
...the document body...
<H2><A name="section1">Introduction</A></H2>
...section 1...
<H2><A name="section2">Some background</A></H2>
...section 2...
<H3><A name="section2.1">On a more personal note</A></H3>
...section 2.1...
We may achieve the same effect by making the header elements
themselves the anchors:
<H1>Table of Contents</H1>
<P><A href="#section1">Introduction</A><BR>
<A href="#section2">Some background</A><BR>
<A href="#section2.1">On a more personal note</A><BR>
...the rest of the table of contents...
...the document body...
<H2 id="section1">Introduction</H2>
...section 1...
<H2 id="section2">Some background</H2>
...section 2...
<H3 id="section2.1">On a more personal note</H3>
...section 2.1...
12.1.2 Other link relationships
By far the most common use of a link is to retrieve another Web
resource, as illustrated in the previous examples. However, authors
may insert links in their documents that express other relationships
between resources than simply "activate this link to visit that
related resource". Links that express other types of relationships
have one or more link types specified in their source anchor.
The roles of a link defined by A or LINK are specified via the rel and
rev attributes.
For instance, links defined by the LINK element may describe the
position of a document within a series of documents. In the following
excerpt, links within the document entitled "Chapter 5" point to the
previous and next chapters:
<HEAD>
...other head information...
<TITLE>Chapter 5</TITLE>
<LINK rel="prev" href="chapter4.html">
<LINK rel="next" href="chapter6.html">
</HEAD>
The link type of the first link is "prev" and that of the second is
"next" (two of several recognized link types). Links specified by LINK
are not rendered with the document's contents, although user agents
may render them in other ways (e.g., as navigation tools).
Even if they are not used for navigation, these links may be
interpreted in interesting ways. For example, a user agent that prints
a series of HTML documents as a single document may use this link
information as the basis of forming a coherent linear document.
Further information is given below on using links for the benefit of
search engines.
12.1.3 Specifying anchors and links
Although several HTML elements and attributes create links to other
resources (e.g., the IMG element, the FORM element, etc.), this
chapter discusses links and anchors created by the LINK and A
elements. The LINK element may only appear in the head of a document.
The A element may only appear in the body.
When the A element's href attribute is set, the element defines a
source anchor for a link that may be activated by the user to retrieve
a Web resource. The source anchor is the location of the A instance
and the destination anchor is the Web resource.
The retrieved resource may be handled by the user agent in several
ways: by opening a new HTML document in the same user agent window,
opening a new HTML document in a different window, starting a new
program to handle the resource, etc. Since the A element has content
(text, images, etc.), user agents may render this content in such a
way as to indicate the presence of a link (e.g., by underlining the
content).
When the name or id attributes of the A element are set, the element
defines an anchor that may be the destination of other links.
Authors may set the name and href attributes simultaneously in the
same A instance.
The LINK element defines a relationship between the current document
and another resource. Although LINK has no content, the relationships
it defines may be rendered by some user agents.
12.1.4 Link titles
The title attribute may be set for both A and LINK to add information
about the nature of a link. This information may be spoken by a user
agent, rendered as a tool tip, cause a change in cursor image, etc.
Thus, we may augment a previous example by supplying a title for each
link:
<BODY>
...some text...
<P>You'll find a lot more in <A href="chapter2.html"
title="Go to chapter two">chapter two</A>.
<A href="./chapter2.html"
title="Get chapter two.">chapter two</A>.
See also this <A href="../images/forest.gif"
title="GIF image of enchanted forest">map of
the enchanted forest.</A>
</BODY>
12.1.5 Internationalization and links
Since links may point to documents encoded with different character
encodings, the A and LINK elements support the charset attribute. This
attribute allows authors to advise user agents about the encoding of
data at the other end of the link.
The hreflang attribute provides user agents with information about the
language of a resource at the end of a link, just as the lang
attribute provides information about the language of an element's
content or attribute values.
Armed with this additional knowledge, user agents should be able to
avoid presenting "garbage" to the user. Instead, they may either
locate resources necessary for the correct presentation of the
document or, if they cannot locate the resources, they should at least
warn the user that the document will be unreadable and explain the
cause.
12.2 The A element
<!ELEMENT A - - (%inline;)* -(A) -- anchor -->
<!ATTLIST A
%attrs; -- %coreattrs, %i18n, %events --
charset %Charset; #IMPLIED -- char encoding of linked resource --
type %ContentType; #IMPLIED -- advisory content type --
name CDATA #IMPLIED -- named link end --
href %URI; #IMPLIED -- URI for linked resource --
hreflang %LanguageCode; #IMPLIED -- language code --
rel %LinkTypes; #IMPLIED -- forward link types --
rev %LinkTypes; #IMPLIED -- reverse link types --
accesskey %Character; #IMPLIED -- accessibility key character --
shape %Shape; rect -- for use with client-side image maps -
-
coords %Coords; #IMPLIED -- for use with client-side image maps -
-
tabindex NUMBER #IMPLIED -- position in tabbing order --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
>
Start tag: required, End tag: required
Attribute definitions
name = cdata [CS]
This attribute names the current anchor so that it may be the
destination of another link. The value of this attribute must
be a unique anchor name. The scope of this name is the current
document. Note that this attribute shares the same name space
as the id attribute.
href = uri [CT]
This attribute specifies the location of a Web resource, thus
defining a link between the current element (the source anchor)
and the destination anchor defined by this attribute.
hreflang = langcode [CI]
This attribute specifies the base language of the resource
designated by href and may only be used when href is specified.
type = content-type [CI]
This attribute gives an advisory hint as to the content type of
the content available at the link target address. It allows
user agents to opt to use a fallback mechanism rather than
fetch the content if they are advised that they will get
content in a content type they do not support.
Authors who use this attribute take responsibility to manage
the risk that it may become inconsistent with the content
available at the link target address.
For the current list of registered content types, please
consult [MIMETYPES].
rel = link-types [CI]
This attribute describes the relationship from the current
document to the anchor specified by the href attribute. The
value of this attribute is a space-separated list of link
types.
rev = link-types [CI]
This attribute is used to describe a reverse link from the
anchor specified by the href attribute to the current document.
The value of this attribute is a space-separated list of link
types.
charset = charset [CI]
This attribute specifies the character encoding of the resource
designated by the link. Please consult the section on character
encodings for more details.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* shape and coords (image maps)
* onfocus, onblur, onclick, ondblclick, onmousedown, onmouseup,
onmouseover, onmousemove, onmouseout, onkeypress, onkeydown,
onkeyup (intrinsic events )
* target (target frame information)
* tabindex (tabbing navigation)
* accesskey (access keys)
Each A element defines an anchor
1. The A element's content defines the position of the anchor.
2. The name attribute names the anchor so that it may be the
destination of zero or more links (see also anchors with id).
3. The href attribute makes this anchor the source anchor of exactly
one link.
Authors may also create an A element that specifies no anchors, i.e.,
that doesn't specify href, name, or id. Values for these attributes
may be set at a later time through scripts.
In the example that follows, the A element defines a link. The source
anchor is the text "W3C Web site" and the destination anchor is
"http://www.w3.org/":
For more information about W3C, please consult the
<A href="http://www.w3.org/">W3C Web site</A>.
This link designates the home page of the World Wide Web Consortium.
When a user activates this link in a user agent, the user agent will
retrieve the resource, in this case, an HTML document.
User agents generally render links in such a way as to make them
obvious to users (underlining, reverse video, etc.). The exact
rendering depends on the user agent. Rendering may vary according to
whether the user has already visited the link or not. A possible
visual rendering of the previous link might be:
For more information about W3C, please consult the W3C Web site.
~~~~~~~~~~~~
To tell user agents explicitly what the character encoding of the
destination page is, set the charset attribute:
For more information about W3C, please consult the
<A href="http://www.w3.org/" charset="ISO-8859-1">W3C Web site</A>
Suppose we define an anchor named "anchor-one" in the file "one.html".
...text before the anchor...
<A name="anchor-one">This is the location of anchor one.</A>
...text after the anchor...
This creates an anchor around the text "This is the location of anchor
one.". Usually, the contents of A are not rendered in any special way
when A defines an anchor only.
Having defined the anchor, we may link to it from the same or another
document. URIs that designate anchors contain a "#" character followed
by the anchor name (the fragment identifier). Here are some examples
of such URIs:
* An absolute URI: http://www.mycompany.com/one.html#anchor-one
* A relative URI: ./one.html#anchor-one or one.html#anchor-one
* When the link is defined in the same document: #anchor-one
Thus, a link defined in the file "two.html" in the same directory as
"one.html" would refer to the anchor as follows:
...text before the link...
For more information, please consult <A href="./one.html#anchor-one"> anchor on
e</A>.
...text after the link...
The A element in the following example specifies a link (with href)
and creates a named anchor (with name) simultaneously:
I just returned from vacation! Here's a
<A name="anchor-two"
href="http://www.somecompany.com/People/Ian/vacation/family.png">
photo of my family at the lake.</A>.
This example contains a link to a different type of Web resource (a
PNG image). Activating the link should cause the image resource to be
retrieved from the Web (and possibly displayed if the system has been
configured to do so).
Note. User agents should be able to find anchors created by empty A
elements, but some fail to do so. For example, some user agents may
not find the "empty-anchor" in the following HTML fragment:
<A name="empty-anchor"></A>
<EM>...some HTML...</EM>
<A href="#empty-anchor">Link to empty anchor</A>
12.2.1 Syntax of anchor names
An anchor name is the value of either the name or id attribute when
used in the context of anchors. Anchor names must observe the
following rules:
* Uniqueness: Anchor names must be unique within a document. Anchor
names that differ only in case may not appear in the same
document.
* String matching: Comparisons between fragment identifiers and
anchor names must be done by exact (case-sensitive) match.
Thus, the following example is correct with respect to string matching
and must be considered a match by user agents:
<P><A href="#xxx">...</A>
...more document...
<P><A name="xxx">...</A>
ILLEGAL EXAMPLE:
The following example is illegal with respect to uniqueness since the
two names are the same except for case:
<P><A name="xxx">...</A>
<P><A name="XXX">...</A>
Although the following excerpt is legal HTML, the behavior of the user
agent is not defined; some user agents may (incorrectly) consider this
a match and others may not.
<P><A href="#xxx">...</A>
...more document...
<P><A name="XXX">...</A>
Anchor names should be restricted to ASCII characters. Please consult
the appendix for more information about non-ASCII characters in URI
attribute values.
12.2.2 Nested links are illegal
Links and anchors defined by the A element must not be nested; an A
element must not contain any other A elements.
Since the DTD defines the LINK element to be empty, LINK elements may
not be nested either.
12.2.3 Anchors with the id attribute
The id attribute may be used to create an anchor at the start tag of
any element (including the A element).
This example illustrates the use of the id attribute to position an
anchor in an H2 element. The anchor is linked to via the A element.
You may read more about this in <A href="#section2">Section Two</A>.
...later in the document
<H2 id="section2">Section Two</H2>
...later in the document
<P>Please refer to <A href="#section2">Section Two</A> above
for more details.
The following example names a destination anchor with the id
attribute:
I just returned from vacation! Here's a
<A id="anchor-two">photo of my family at the lake.</A>.
The id and name attributes share the same name space. This means that
they cannot both define an anchor with the same name in the same
document. It is permissible to use both attributes to specify an
element's unique identifier for the following elements: A, APPLET,
FORM, FRAME, IFRAME, IMG, and MAP. When both attributes are used on a
single element, their values must be identical.
ILLEGAL EXAMPLE:
The following excerpt is illegal HTML since these attributes declare
the same name twice in the same document.
<A href="#a1">...</A>
...
<H1 id="a1">
...pages and pages...
<A name="a1"></A>
The following example illustrates that id and name must be the same
when both appear in an element's start tag:
<P><A name="a1" id="a1" href="#a1">...</A>
Because of its specification in the HTML DTD, the name attribute may
contain character references. Thus, the value Dürst is a valid
name attribute value, as is Dürst . The id attribute, on the
other hand, may not contain character references.
Use id or name? Authors should consider the following issues when
deciding whether to use id or name for an anchor name:
* The id attribute can act as more than just an anchor name (e.g.,
style sheet selector, processing identifier, etc.).
* Some older user agents don't support anchors created with the id
attribute.
* The name attribute allows richer anchor names (with entities).
12.2.4 Unavailable and unidentifiable resources
A reference to an unavailable or unidentifiable resource is an error.
Although user agents may vary in how they handle such an error, we
recommend the following behavior:
* If a user agent cannot locate a linked resource, it should alert
the user.
* If a user agent cannot identify the type of a linked resource, it
should still attempt to process it. It should alert the user and
may allow the user to intervene and identify the document type.
12.3 Document relationships: the LINK element
<!ELEMENT LINK - O EMPTY -- a media-independent link -->
<!ATTLIST LINK
%attrs; -- %coreattrs, %i18n, %events --
charset %Charset; #IMPLIED -- char encoding of linked resource --
href %URI; #IMPLIED -- URI for linked resource --
hreflang %LanguageCode; #IMPLIED -- language code --
type %ContentType; #IMPLIED -- advisory content type --
rel %LinkTypes; #IMPLIED -- forward link types --
rev %LinkTypes; #IMPLIED -- reverse link types --
media %MediaDesc; #IMPLIED -- for rendering on these media --
>
Start tag: required, End tag: forbidden
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information )
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events )
* href, hreflang, type, rel, rev (links and anchors)
* target (target frame information)
* media (header style information)
* charset(character encodings)
This element defines a link. Unlike A, it may only appear in the HEAD
section of a document, although it may appear any number of times.
Although LINK has no content, it conveys relationship information that
may be rendered by user agents in a variety of ways (e.g., a tool-bar
with a drop-down menu of links).
This example illustrates how several LINK definitions may appear in
the HEAD section of a document. The current document is
"Chapter2.html". The rel attribute specifies the relationship of the
linked document with the current document. The values "Index", "Next",
and "Prev" are explained in the section on link types.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>Chapter 2</TITLE>
<LINK rel="Index" href="../index.html">
<LINK rel="Next" href="Chapter3.html">
<LINK rel="Prev" href="Chapter1.html">
</HEAD>
...the rest of the document...
12.3.1 Forward and reverse links
The rel and rev attributes play complementary roles -- the rel
attribute specifies a forward link and the rev attribute specifies a
reverse link.
Consider two documents A and B.
Document A: <LINK href="docB" rel="foo">
Has exactly the same meaning as:
Document B: <LINK href="docA" rev="foo">
Both attributes may be specified simultaneously.
12.3.2 Links and external style sheets
When the LINK element links an external style sheet to a document, the
type attribute specifies the style sheet language and the media
attribute specifies the intended rendering medium or media. User
agents may save time by retrieving from the network only those style
sheets that apply to the current device.
Media types are further discussed in the section on style sheets.
12.3.3 Links and search engines
Authors may use the LINK element to provide a variety of information
to search engines, including:
* Links to alternate versions of a document, written in another
human language.
* Links to alternate versions of a document, designed for different
media, for instance a version especially suited for printing.
* Links to the starting page of a collection of documents.
The examples below illustrate how language information, media types,
and link types may be combined to improve document handling by search
engines.
In the following example, we use the hreflang attribute to tell search
engines where to find Dutch, Portuguese, and Arabic versions of a
document. Note the use of the charset attribute for the Arabic manual.
Note also the use of the lang attribute to indicate that the value of
the title attribute for the LINK element designating the French manual
is in French.
<HEAD>
<TITLE>The manual in English</TITLE>
<LINK title="The manual in Dutch"
type="text/html"
rel="alternate"
hreflang="nl"
href="http://someplace.com/manual/dutch.html">
<LINK title="The manual in Portuguese"
type="text/html"
rel="alternate"
hreflang="pt"
href="http://someplace.com/manual/portuguese.html">
<LINK title="The manual in Arabic"
type="text/html"
rel="alternate"
charset="ISO-8859-6"
hreflang="ar"
href="http://someplace.com/manual/arabic.html">
<LINK lang="fr" title="La documentation en Français"
type="text/html"
rel="alternate"
hreflang="fr"
href="http://someplace.com/manual/french.html">
</HEAD>
In the following example, we tell search engines where to find the
printed version of a manual.
<HEAD>
<TITLE>Reference manual</TITLE>
<LINK media="print" title="The manual in postscript"
type="application/postscript"
rel="alternate"
href="http://someplace.com/manual/postscript.ps">
</HEAD>
In the following example, we tell search engines where to find the
front page of a collection of documents.
<HEAD>
<TITLE>Reference manual -- Page 5</TITLE>
<LINK rel="Start" title="The first page of the manual"
type="text/html"
href="http://someplace.com/manual/start.html">
</HEAD>
Further information is given in the notes in the appendix on helping
search engines index your Web site.
12.4 Path information: the BASE element
<!ELEMENT BASE - O EMPTY -- document base URI -->
<!ATTLIST BASE
href %URI; #REQUIRED -- URI that acts as base URI --
>
Start tag: required, End tag: forbidden
Attribute definitions
href = uri [CT]
This attribute specifies an absolute URI that acts as the base
URI for resolving relative URIs.
Attributes defined elsewhere
* target (target frame information)
In HTML, links and references to external images, applets,
form-processing programs, style sheets, etc. are always specified by a
URI. Relative URIs are resolved according to a base URI, which may
come from a variety of sources. The BASE element allows authors to
specify a document's base URI explicitly.
When present, the BASE element must appear in the HEAD section of an
HTML document, before any element that refers to an external source.
The path information specified by the BASE element only affects URIs
in the document where the element appears.
For example, given the following BASE declaration and A declaration:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>Our Products</TITLE>
<BASE href="http://www.aviary.com/products/intro.html">
</HEAD>
<BODY>
<P>Have you seen our <A href="../cages/birds.gif">Bird Cages</A>?
</BODY>
</HTML>
the relative URI "../cages/birds.gif" would resolve to:
http://www.aviary.com/cages/birds.gif
12.4.1 Resolving relative URIs
User agents must calculate the base URI for resolving relative URIs
according to [RFC1808], section 3. The following describes how
[RFC1808] applies specifically to HTML.
User agents must calculate the base URI according to the following
precedences (highest priority to lowest):
1. The base URI is set by the BASE element.
2. The base URI is given by meta data discovered during a protocol
interaction, such as an HTTP header (see [RFC2616]).
3. By default, the base URI is that of the current document. Not all
HTML documents have a base URI (e.g., a valid HTML document may
appear in an email and may not be designated by a URI). Such HTML
documents are considered erroneous if they contain relative URIs
and rely on a default base URI.
Additionally, the OBJECT and APPLET elements define attributes that
take precedence over the value set by the BASE element. Please consult
the definitions of these elements for more information about URI
issues specific to them.
Note. For versions of HTTP that define a Link header, user agents
should handle these headers exactly as LINK elements in the document.
HTTP 1.1 as defined by [RFC2616] does not include a Link header field
(refer to section 19.6.3).
13 Objects, Images, and Applets
Contents
1. Introduction to objects, images, and applets
2. Including an image: the IMG element
3. Generic inclusion: the OBJECT element
1. Rules for rendering objects
2. Object initialization: the PARAM element
3. Global naming schemes for objects
4. Object declarations and instantiations
4. Including an applet: the APPLET element
5. Notes on embedded documents
6. Image maps
1. Client-side image maps: the MAP and AREA elements
o Client-side image map examples
2. Server-side image maps
7. Visual presentation of images, objects, and applets
1. Width and height
2. White space around images and objects
3. Borders
4. Alignment
8. How to specify alternate text
13.1 Introduction to objects, images, and applets
HTML's multimedia features allow authors to include images, applets
(programs that are automatically downloaded and run on the user's
machine), video clips, and other HTML documents in their pages.
For example, to include a PNG image in a document, authors may write:
<BODY>
<P>Here's a closeup of the Grand Canyon:
<OBJECT data="canyon.png" type="image/png">
This is a <EM>closeup</EM> of the Grand Canyon.
</OBJECT>
</BODY>
Previous versions of HTML allowed authors to include images (via IMG)
and applets (via APPLET). These elements have several limitations:
* They fail to solve the more general problem of how to include new
and future media types.
* The APPLET element only works with Java-based applets. This
element is deprecated in favor of OBJECT.
* They pose accessibility problems.
To address these issues, HTML 4 introduces the OBJECT element, which
offers an all-purpose solution to generic object inclusion. The OBJECT
element allows HTML authors to specify everything required by an
object for its presentation by a user agent: source code, initial
values, and run-time data. In this specification, the term "object" is
used to describe the things that people want to place in HTML
documents; other commonly used terms for these things are: applets,
plug-ins, media handlers, etc.
The new OBJECT element thus subsumes some of the tasks carried out by
existing elements. Consider the following chart of functionalities:
Type of inclusion Specific element Generic element
Image IMG OBJECT
Applet APPLET (Deprecated.) OBJECT
Another HTML document IFRAME OBJECT
The chart indicates that each type of inclusion has a specific and a
general solution. The generic OBJECT element will serve as the
solution for implementing future media types.
To include images, authors may use the OBJECT element or the IMG
element.
To include applets, authors should use the OBJECT element as the
APPLET element is deprecated.
To include one HTML document in another, authors may use either the
new IFRAME element or the OBJECT element. In both cases, the embedded
document remains independent of the main document. Visual user agents
may present the embedded document in a distinct window within the main
document. Please consult the notes on embedded documents for a
comparison of OBJECT and IFRAME for document inclusion.
Images and other included objects may have hyperlinks associated with
them, both through the standard linking mechanisms, but also via image
maps. An image map specifies active geometric regions of an included
object and assigns a link to each region. When activated, these links
may cause a document to be retrieved, may run a program on the server,
etc.
In the following sections, we discuss the various mechanisms available
to authors for multimedia inclusions and creating image maps for those
inclusions.
13.2 Including an image: the IMG element
<!-- To avoid problems with text-only UAs as well as
to make image content understandable and navigable
to users of non-visual UAs, you need to provide
a description with ALT, and avoid server-side image maps -->
<!ELEMENT IMG - O EMPTY -- Embedded image -->
<!ATTLIST IMG
%attrs; -- %coreattrs, %i18n, %events --
src %URI; #REQUIRED -- URI of image to embed --
alt %Text; #REQUIRED -- short description --
longdesc %URI; #IMPLIED -- link to long description
(complements alt) --
name CDATA #IMPLIED -- name of image for scripting --
height %Length; #IMPLIED -- override height --
width %Length; #IMPLIED -- override width --
usemap %URI; #IMPLIED -- use client-side image map --
ismap (ismap) #IMPLIED -- use server-side image map --
>
Start tag: required, End tag: forbidden
Attribute definitions
src = uri [CT]
This attribute specifies the location of the image resource.
Examples of widely recognized image formats include GIF, JPEG,
and PNG.
longdesc = uri [CT]
This attribute specifies a link to a long description of the
image. This description should supplement the short description
provided using the alt attribute. When the image has an
associated image map, this attribute should provide information
about the image map's contents. This is particularly important
for server-side image maps. Since an IMG element may be within
the content of an A element, the user agent's mechanism in the
user interface for accessing the "longdesc" resource of the
former must be different than the mechanism for accessing the
href resource of the latter.
name = cdata [CI]
This attribute names the element so that it may be referred to
from style sheets or scripts. Note. This attribute has been
included for backwards compatibility. Applications should use
the id attribute to identify elements.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* alt (alternate text)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
* ismap, usemap (client side image maps)
* align, width, height, border, hspace, vspace (visual presentation
of objects, images, and applets)
The IMG element embeds an image in the current document at the
location of the element's definition. The IMG element has no content;
it is usually replaced inline by the image designated by the src
attribute, the exception being for left or right-aligned images that
are "floated" out of line.
In an earlier example, we defined a link to a family photo. Here, we
insert the photo directly into the current document:
<BODY>
<P>I just returned from vacation! Here's a photo of my family at the lake:
<IMG src="http://www.somecompany.com/People/Ian/vacation/family.png"
alt="A photo of my family at the lake.">
</BODY>
This inclusion may also be achieved with the OBJECT element as
follows:
<BODY>
<P>I just returned from vacation! Here's a photo of my family at the lake:
<OBJECT data="http://www.somecompany.com/People/Ian/vacation/family.png"
type="image/png">
A photo of my family at the lake.
</OBJECT>
</BODY>
The alt attribute specifies alternate text that is rendered when the
image cannot be displayed (see below for information on how to specify
alternate text ). User agents must render alternate text when they
cannot support images, they cannot support a certain image type or
when they are configured not to display images.
The following example shows how the longdesc attribute can be used to
link to a richer description:
<BODY>
<P>
<IMG src="sitemap.gif"
alt="HP Labs Site Map"
longdesc="sitemap.html">
</BODY>
The alt attribute provides a short description of the image. This
should be sufficient to allow users to decide whether they want to
follow the link given by the longdesc attribute to the longer
description, here "sitemap.html".
Please consult the section on the visual presentation of objects,
images, and applets for information about image size, alignment, and
borders.
13.3 Generic inclusion: the OBJECT element
<!ELEMENT OBJECT - - (PARAM | %flow;)*
-- generic embedded object -->
<!ATTLIST OBJECT
%attrs; -- %coreattrs, %i18n, %events --
declare (declare) #IMPLIED -- declare but don't instantiate flag --
classid %URI; #IMPLIED -- identifies an implementation --
codebase %URI; #IMPLIED -- base URI for classid, data, archive--
data %URI; #IMPLIED -- reference to object's data --
type %ContentType; #IMPLIED -- content type for data --
codetype %ContentType; #IMPLIED -- content type for code --
archive CDATA #IMPLIED -- space-separated list of URIs --
standby %Text; #IMPLIED -- message to show while loading --
height %Length; #IMPLIED -- override height --
width %Length; #IMPLIED -- override width --
usemap %URI; #IMPLIED -- use client-side image map --
name CDATA #IMPLIED -- submit as part of form --
tabindex NUMBER #IMPLIED -- position in tabbing order --
>
Start tag: required, End tag: required
Attribute definitions
classid = uri [CT]
This attribute may be used to specify the location of an
object's implementation via a URI. It may be used together
with, or as an alternative to the data attribute, depending on
the type of object involved.
codebase = uri [CT]
This attribute specifies the base path used to resolve relative
URIs specified by the classid, data, and archive attributes.
When absent, its default value is the base URI of the current
document.
codetype = content-type [CI]
This attribute specifies the content type of data expected when
downloading the object specified by classid. This attribute is
optional but recommended when classid is specified since it
allows the user agent to avoid loading information for
unsupported content types. When absent, it defaults to the
value of the type attribute.
data = uri [CT]
This attribute may be used to specify the location of the
object's data, for instance image data for objects defining
images, or more generally, a serialized form of an object which
can be used to recreate it. If given as a relative URI, it
should be interpreted relative to the codebase attribute.
type = content-type [CI]
This attribute specifies the content type for the data
specified by data. This attribute is optional but recommended
when data is specified since it allows the user agent to avoid
loading information for unsupported content types. If the value
of this attribute differs from the HTTP Content-Type returned
by the server when the object is retrieved, the HTTP
Content-Type takes precedence.
archive = uri-list [CT]
This attribute may be used to specify a space-separated list of
URIs for archives containing resources relevant to the object,
which may include the resources specified by the classid and
data attributes. Preloading archives will generally result in
reduced load times for objects. Archives specified as relative
URIs should be interpreted relative to the codebase attribute.
declare [CI]
When present, this boolean attribute makes the current OBJECT
definition a declaration only. The object must be instantiated
by a subsequent OBJECT definition referring to this
declaration.
standby = text [CS]
This attribute specifies a message that a user agent may render
while loading the object's implementation and data.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
* tabindex (tabbing navigation)
* usemap (client side image maps)
* name (form submission)
* align, width, height, border, hspace, vspace (visual presentation
of objects, images, and applets)
Most user agents have built-in mechanisms for rendering common data
types such as text, GIF images, colors, fonts, and a handful of
graphic elements. To render data types they don't support natively,
user agents generally run external applications. The OBJECT element
allows authors to control whether data should be rendered externally
or by some program, specified by the author, that renders the data
within the user agent.
In the most general case, an author may need to specify three types of
information:
* The implementation of the included object. For instance, if the
included object is a clock applet, the author must indicate the
location of the applet's executable code.
* The data to be rendered. For instance, if the included object is a
program that renders font data, the author must indicate the
location of that data.
* Additional values required by the object at run-time. For example,
some applets may require initial values for parameters.
The OBJECT element allows authors to specify all three types of data,
but authors may not have to specify all three at once. For example,
some objects may not require data (e.g., a self-contained applet that
performs a small animation). Others may not require run-time
initialization. Still others may not require additional implementation
information, i.e., the user agent itself may already know how to
render that type of data (e.g., GIF images).
Authors specify an object's implementation and the location of the
data to be rendered via the OBJECT element. To specify run-time
values, however, authors use the PARAM element, which is discussed in
the section on object initialization.
The OBJECT element may also appear in the content of the HEAD element.
Since user agents generally do not render elements in the HEAD,
authors should ensure that any OBJECT elements in the HEAD do not
specify content that may be rendered. Please consult the section on
sharing frame data for an example of including the OBJECT element in
the HEAD element.
Please consult the section on form controls for information about
OBJECT elements in forms.
This document does not specify the behavior of OBJECT elements that
use both the classid attribute to identify an implementation and the
data attribute to specify data for that implementation. In order to
ensure portability, authors should use the PARAM element to tell
implementations where to retrieve additional data.
13.3.1 Rules for rendering objects
A user agent must interpret an OBJECT element according to the
following precedence rules:
1. The user agent must first try to render the object. It should not
render the element's contents, but it must examine them in case
the element contains any direct children that are PARAM elements
(see object initialization) or MAP elements (see client-side image
maps).
2. If the user agent is not able to render the object for whatever
reason (configured not to, lack of resources, wrong architecture,
etc.), it must try to render its contents.
Authors should not include content in OBJECT elements that appear in
the HEAD element.
In the following example, we insert an analog clock applet in a
document via the OBJECT element. The applet, written in the Python
language, requires no additional data or run-time values. The classid
attribute specifies the location of the applet:
<P><OBJECT classid="http://www.miamachina.it/analogclock.py">
</OBJECT>
Note that the clock will be rendered as soon as the user agent
interprets this OBJECT declaration. It is possible to delay rendering
of an object by first declaring the object (described below).
Authors should complete this declaration by including alternate text
as the contents of OBJECT in case the user agent cannot render the
clock.
<P><OBJECT classid="http://www.miamachina.it/analogclock.py">
An animated clock.
</OBJECT>
One significant consequence of the OBJECT element's design is that it
offers a mechanism for specifying alternate object renderings; each
embedded OBJECT declaration may specify alternate content types. If a
user agent cannot render the outermost OBJECT, it tries to render the
contents, which may be another OBJECT element, etc.
In the following example, we embed several OBJECT declarations to
illustrate how alternate renderings work. A user agent will attempt to
render the first OBJECT element it can, in the following order: (1) an
Earth applet written in the Python language, (2) an MPEG animation of
the Earth, (3) a GIF image of the Earth, (4) alternate text.
<P> <!-- First, try the Python applet -->
<OBJECT title="The Earth as seen from space"
classid="http://www.observer.mars/TheEarth.py">
<!-- Else, try the MPEG video -->
<OBJECT data="TheEarth.mpeg" type="application/mpeg">
<!-- Else, try the GIF image -->
<OBJECT data="TheEarth.gif" type="image/gif">
<!-- Else render the text -->
The <STRONG>Earth</STRONG> as seen from space.
</OBJECT>
</OBJECT>
</OBJECT>
The outermost declaration specifies an applet that requires no data or
initial values. The second declaration specifies an MPEG animation
and, since it does not define the location of an implementation to
handle MPEG, relies on the user agent to handle the animation. We also
set the type attribute so that a user agent that knows it cannot
render MPEG will not bother to retrieve "TheEarth.mpeg" from the
network. The third declaration specifies the location of a GIF file
and furnishes alternate text in case all other mechanisms fail.
Inline vs. external data. Data to be rendered may be supplied in two
ways: inline and from an external resource. While the former method
will generally lead to faster rendering, it is not convenient when
rendering large quantities of data.
Here's an example that illustrates how inline data may be fed to an
OBJECT:
<P>
<OBJECT id="clock1"
classid="clsid:663C8FEF-1EF9-11CF-A3DB-080036F12502"
data="data:application/x-oleobject;base64, ...base64 data...">
A clock.
</OBJECT>
Please consult the section on the visual presentation of objects,
images, and applets for information about object size, alignment, and
borders.
13.3.2 Object initialization: the PARAM element
<!ELEMENT PARAM - O EMPTY -- named property value -->
<!ATTLIST PARAM
id ID #IMPLIED -- document-wide unique id --
name CDATA #REQUIRED -- property name --
value CDATA #IMPLIED -- property value --
valuetype (DATA|REF|OBJECT) DATA -- How to interpret value --
type %ContentType; #IMPLIED -- content type for value
when valuetype=ref --
>
Start tag: required, End tag: forbidden
Attribute definitions
name = cdata
This attribute defines the name of a run-time parameter,
assumed to be known by the inserted object. Whether the
property name is case-sensitive depends on the specific object
implementation.
value = cdata
This attribute specifies the value of a run-time parameter
specified by name. Property values have no meaning to HTML;
their meaning is determined by the object in question.
valuetype = data|ref|object [CI]
This attribute specifies the type of the value attribute.
Possible values:
+ data: This is default value for the attribute. It means that
the value specified by value will be evaluated and passed to
the object's implementation as a string.
+ ref: The value specified by value is a URI that designates a
resource where run-time values are stored. This allows
support tools to identify URIs given as parameters. The URI
must be passed to the object as is, i.e., unresolved.
+ object: The value specified by value is an identifier that
refers to an OBJECT declaration in the same document. The
identifier must be the value of the id attribute set for the
declared OBJECT element.
type = content-type [CI]
This attribute specifies the content type of the resource
designated by the value attribute only in the case where
valuetype is set to "ref". This attribute thus specifies for
the user agent, the type of values that will be found at the
URI designated by value.
Attributes defined elsewhere
* id (document-wide identifiers)
PARAM elements specify a set of values that may be required by an
object at run-time. Any number of PARAM elements may appear in the
content of an OBJECT or APPLET element, in any order, but must be
placed at the start of the content of the enclosing OBJECT or APPLET
element.
The syntax of names and values is assumed to be understood by the
object's implementation. This document does not specify how user
agents should retrieve name/value pairs nor how they should interpret
parameter names that appear twice.
We return to the clock example to illustrate the use of PARAM: suppose
that the applet is able to handle two run-time parameters that define
its initial height and width. We can set the initial dimensions to
40x40 pixels with two PARAM elements.
<P><OBJECT classid="http://www.miamachina.it/analogclock.py">
<PARAM name="height" value="40" valuetype="data">
<PARAM name="width" value="40" valuetype="data">
This user agent cannot render Python applications.
</OBJECT>
In the following example, run-time data for the object's "Init_values"
parameter is specified as an external resource (a GIF file). The value
of the valuetype attribute is thus set to "ref" and the value is a URI
designating the resource.
<P><OBJECT classid="http://www.gifstuff.com/gifappli"
standby="Loading Elvis...">
<PARAM name="Init_values"
value="./images/elvis.gif">
valuetype="ref">
</OBJECT>
Note that we have also set the standby attribute so that the user
agent may display a message while the rendering mechanism loads.
When an OBJECT element is rendered, user agents must search the
content for only those PARAM elements that are direct children and
"feed" them to the OBJECT.
Thus, in the following example, if "obj1" is rendered, "param1"
applies to "obj1" (and not "obj2"). If "obj1" is not rendered and
"obj2" is, "param1" is ignored, and "param2" applies to "obj2". If
neither OBJECT is rendered, neither PARAM applies.
<P>
<OBJECT id="obj1">
<PARAM name="param1">
<OBJECT id="obj2">
<PARAM name="param2">
</OBJECT>
</OBJECT>
13.3.3 Global naming schemes for objects
The location of an object's implementation is given by a URI. As we
discussed in the introduction to URIs, the first segment of an
absolute URI specifies the naming scheme used to transfer the data
designated by the URI. For HTML documents, this scheme is frequently
"http". Some applets might employ other naming schemes. For instance,
when specifying a Java applet, authors may use URIs that begin with
"java" and for ActiveX applets, authors may use "clsid".
In the following example, we insert a Java applet into an HTML
document.
<P><OBJECT classid="java:program.start">
</OBJECT>
By setting the codetype attribute, a user agent can decide whether to
retrieve the Java application based on its ability to do so.
<OBJECT codetype="application/java-archive"
classid="java:program.start">
</OBJECT>
Some rendering schemes require additional information to identify
their implementation and must be told where to find that information.
Authors may give path information to the object's implementation via
the codebase attribute.
<OBJECT codetype="application/java-archive"
classid="java:program.start">
codebase="http://foooo.bar.com/java/myimplementation/"
</OBJECT>
The following example specifies (with the classid attribute) an
ActiveX object via a URI that begins with the naming scheme "clsid".
The data attribute locates the data to render (another clock).
<P><OBJECT classid="clsid:663C8FEF-1EF9-11CF-A3DB-080036F12502"
data="http://www.acme.com/ole/clock.stm">
This application is not supported.
</OBJECT>
13.3.4 Object declarations and instantiations
The preceding examples have only illustrated isolated object
definitions. When a document is to contain more than one instance of
the same object, it is possible to separate the declaration of the
object from its instantiations. Doing so has several advantages:
* Data may be retrieved from the network by the user agent one time
(during the declaration) and reused for each instantiation.
* It is possible to instantiate an object from a location other than
the object's declaration, for example, from a link.
* It is possible to specify objects as run-time data for other
objects.
To declare an object so that it is not executed when read by the user
agent, set the boolean declare attribute in the OBJECT element. At the
same time, authors must identify the declaration by setting the id
attribute in the OBJECT element to a unique value. Later
instantiations of the object will refer to this identifier.
A declared OBJECT must appear in a document before the first instance
of that OBJECT.
An object defined with the declare attribute is instantiated every
time an element that refers to that object requires it to be rendered
(e.g., a link that refers to it is activated, an object that refers to
it is activated, etc.).
In the following example, we declare an OBJECT and cause it to be
instantiated by referring to it from a link. Thus, the object can be
activated by clicking on some highlighted text, for example.
<P><OBJECT declare
id="earth.declaration"
data="TheEarth.mpeg"
type="application/mpeg">
The <STRONG>Earth</STRONG> as seen from space.
</OBJECT>
...later in the document...
<P>A neat <A href="#earth.declaration"> animation of The Earth!</A>
The following example illustrates how to specify run-time values that
are other objects. In this example, we send text (a poem, in fact) to
a hypothetical mechanism for viewing poems. The object recognizes a
run-time parameter named "font" (say, for rendering the poem text in a
certain font). The value for this parameter is itself an object that
inserts (but does not render) the font object. The relationship
between the font object and the poem viewer object is achieved by (1)
assigning the id "tribune" to the font object declaration and (2)
referring to it from the PARAM element of the poem viewer object (with
valuetype and value).
<P><OBJECT declare
id="tribune"
type="application/x-webfont"
data="tribune.gif">
</OBJECT>
...view the poem in KublaKhan.txt here...
<P><OBJECT classid="http://foo.bar.com/poem_viewer"
data="KublaKhan.txt">
<PARAM name="font" valuetype="object" value="#tribune">
<P>You're missing a really cool poem viewer ...
</OBJECT>
User agents that don't support the declare attribute must render the
contents of the OBJECT declaration.
13.4 Including an applet: the APPLET element
APPLET is deprecated (with all its attributes) in favor of OBJECT.
See the Transitional DTD for the formal definition.
Attribute definitions
codebase = uri [CT]
This attribute specifies the base URI for the applet. If this
attribute is not specified, then it defaults the same base URI
as for the current document. Values for this attribute may only
refer to subdirectories of the directory containing the current
document. Note. While the restriction on subdirectories is a
departure from common practice and the HTML 3.2 specification,
the HTML Working Group has chosen to leave the restriction in
this version of the specification for security reasons.
code = cdata [CS]
This attribute specifies either the name of the class file that
contains the applet's compiled applet subclass or the path to
get the class, including the class file itself. It is
interpreted with respect to the applet's codebase. One of code
or object must be present.
name = cdata [CS]
This attribute specifies a name for the applet instance, which
makes it possible for applets on the same page to find (and
communicate with) each other.
archive = uri-list [CT]
This attribute specifies a comma-separated list of URIs for
archives containing classes and other resources that will be
"preloaded". The classes are loaded using an instance of an
AppletClassLoader with the given codebase. Relative URIs for
archives are interpreted with respect to the applet's codebase.
Preloading resources can significantly improve the performance
of applets.
object = cdata [CS]
This attribute names a resource containing a serialized
representation of an applet's state. It is interpreted relative
to the applet's codebase. The serialized data contains the
applet's class name but not the implementation. The class name
is used to retrieve the implementation from a class file or
archive.
When the applet is "deserialized" the start() method is invoked
but not the init() method. Attributes valid when the original
object was serialized are not restored. Any attributes passed
to this APPLET instance will be available to the applet.
Authors should use this feature with extreme caution. An applet
should be stopped before it is serialized.
Either code or object must be present. If both code and object
are given, it is an error if they provide different class
names.
width = length [CI]
This attribute specifies the initial width of the applet's
display area (excluding any windows or dialogs that the applet
creates).
height = length [CI]
This attribute specifies the initial height of the applet's
display area (excluding any windows or dialogs that the applet
creates).
Attributes defined elsewhere
* id, class (document-wide identifiers)
* title (element title)
* style (inline style information)
* alt (alternate text)
* align, hspace, vspace (visual presentation of objects, images, and
applets)
This element, supported by all Java-enabled browsers, allows designers
to embed a Java applet in an HTML document. It has been deprecated in
favor of the OBJECT element.
The content of the APPLET acts as alternate information for user
agents that don't support this element or are currently configured not
to support applets. User agents must ignore the content otherwise.
DEPRECATED EXAMPLE:
In the following example, the APPLET element includes a Java applet in
the document. Since no codebase is supplied, the applet is assumed to
be in the same directory as the current document.
<APPLET code="Bubbles.class" width="500" height="500">
Java applet that draws animated bubbles.
</APPLET>
This example may be rewritten with OBJECT as follows:
<P><OBJECT codetype="application/java"
classid="java:Bubbles.class"
width="500" height="500">
Java applet that draws animated bubbles.
</OBJECT>
Initial values may be supplied to the applet via the PARAM element.
DEPRECATED EXAMPLE:
The following sample Java applet:
<APPLET code="AudioItem" width="15" height="15">
<PARAM name="snd" value="Hello.au|Welcome.au">
Java applet that plays a welcoming sound.
</APPLET>
may be rewritten as follows with OBJECT:
<OBJECT codetype="application/java"
classid="AudioItem"
width="15" height="15">
<PARAM name="snd" value="Hello.au|Welcome.au">
Java applet that plays a welcoming sound.
</OBJECT>
13.5 Notes on embedded documents
Sometimes, rather than linking to a document, an author may want to
embed it directly into a primary HTML document. Authors may use either
the IFRAME element or the OBJECT element for this purpose, but the
elements differ in some ways. Not only do the two elements have
different content models, the IFRAME element may be a target frame
(see the section on specifying target frame information for details)
and may be "selected" by a user agent as the focus for printing,
viewing HTML source, etc. User agents may render selected frames
elements in ways that distinguish them from unselected frames (e.g.,
by drawing a border around the selected frame).
An embedded document is entirely independent of the document in which
it is embedded. For instance, relative URIs within the embedded
document resolve according to the base URI of the embedded document,
not that of the main document. An embedded document is only rendered
within another document (e.g., in a subwindow); it remains otherwise
independent.
For instance, the following line embeds the contents of embed_me.html
at the location where the OBJECT definition occurs.
...text before...
<OBJECT data="embed_me.html">
Warning: embed_me.html could not be embedded.
</OBJECT>
...text after...
Recall that the contents of OBJECT must only be rendered if the file
specified by the data attribute cannot be loaded.
The behavior of a user agent in cases where a file includes itself is
not defined.
13.6 Image maps
Image maps allow authors to specify regions of an image or object and
assign a specific action to each region (e.g., retrieve a document,
run a program, etc.) When the region is activated by the user, the
action is executed.
An image map is created by associating an object with a specification
of sensitive geometric areas on the object.
There are two types of image maps:
* Client-side. When a user activates a region of a client-side image
map with a mouse, the pixel coordinates are interpreted by the
user agent. The user agent selects a link that was specified for
the activated region and follows it.
* Server-side. When a user activates a region of a server-side image
map with a mouse, the pixel coordinates of the click are sent to
the server-side agent specified by the href attribute of the A
element. The server-side agent interprets the coordinates and
performs some action.
Client-side image maps are preferred over server-side image maps for
at least two reasons: they are accessible to people browsing with
non-graphical user agents and they offer immediate feedback as to
whether or not the pointer is over an active region.
13.6.1 Client-side image maps: the MAP and AREA elements
<!ELEMENT MAP - - ((%block;) | AREA)+ -- client-side image map -->
<!ATTLIST MAP
%attrs; -- %coreattrs, %i18n, %events --
name CDATA #REQUIRED -- for reference by usemap --
>
Start tag: required, End tag: required
<!ELEMENT AREA - O EMPTY -- client-side image map area -->
<!ATTLIST AREA
%attrs; -- %coreattrs, %i18n, %events --
shape %Shape; rect -- controls interpretation of coords --
coords %Coords; #IMPLIED -- comma-separated list of lengths --
href %URI; #IMPLIED -- URI for linked resource --
nohref (nohref) #IMPLIED -- this region has no action --
alt %Text; #REQUIRED -- short description --
tabindex NUMBER #IMPLIED -- position in tabbing order --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
>
Start tag: required, End tag: forbidden
MAP attribute definitions
name = cdata [CI]
This attribute assigns a name to the image map defined by a MAP
element.
AREA attribute definitions
shape = default|rect|circle|poly [CI]
This attribute specifies the shape of a region. Possible
values:
+ default: Specifies the entire region.
+ rect: Define a rectangular region.
+ circle: Define a circular region.
+ poly: Define a polygonal region.
coords = coordinates [CN]
This attribute specifies the position and shape on the screen.
The number and order of values depends on the shape being
defined. Possible combinations:
+ rect: left-x, top-y, right-x, bottom-y.
+ circle: center-x, center-y, radius. Note. When the radius
value is a percentage value, user agents should calculate the
final radius value based on the associated object's width and
height. The radius should be the smaller value of the two.
+ poly: x1, y1, x2, y2, ..., xN, yN. The first x and y
coordinate pair and the last should be the same to close the
polygon. When these coordinate values are not the same, user
agents should infer an additional coordinate pair to close
the polygon.
Coordinates are relative to the top, left corner of the object.
All values are lengths. All values are separated by commas.
nohref [CI]
When set, this boolean attribute specifies that a region has no
associated link.
Attribute to associate an image map with an element
usemap = uri [CT]
This attribute associates an image map with an element. The
image map is defined by a MAP element. The value of usemap must
match the value of the name attribute of the associated MAP
element.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* name (submitting objects with forms)
* alt (alternate text)
* href (anchor reference) target (frame target information)
* tabindex (tabbing navigation)
* accesskey (access keys)
* shape (image maps)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup, onfocus,
onblur (intrinsic events)
The MAP element specifies a client-side image map (or other navigation
mechanism) that may be associated with another elements (IMG, OBJECT,
or INPUT). An image map is associated with an element via the
element's usemap attribute. The MAP element may be used without an
associated image for general navigation mechanisms.
The presence of the usemap attribute for an OBJECT implies that the
object being included is an image. Furthermore, when the OBJECT
element has an associated client-side image map, user agents may
implement user interaction with the OBJECT solely in terms of the
client-side image map. This allows user agents (such as an audio
browser or robot) to interact with the OBJECT without having to
process it; the user agent may even elect not to retrieve (or process)
the object. When an OBJECT has an associated image map, authors should
not expect that the object will be retrieved or processed by every
user agent.
The MAP element content model allows authors to combine the following:
1. One or more AREA elements. These elements have no content but
specify the geometric regions of the image map and the link
associated with each region. Note that user agents do not
generally render AREA elements. Therefore, authors must provide
alternate text for each AREA with the alt attribute (see below for
information on how to specify alternate text).
2. Block-level content. This content should include A elements that
specify the geometric regions of the image map and the link
associated with each region. Note that the user agent should
render block-level content of a MAP element. Authors should use
this method to create more accessible documents.
When a MAP element contains mixed content (both AREA elements and
block-level content), user agents must ignore the AREA elements.
Authors should specify an image maps's geometry completely with AREA
elements, or completely with A elements, or completely with both if
content is mixed. Authors may wish to mix content so that older user
agents will handle map geometries specified by AREA elements and new
user agents will take advantage of richer block content.
If two or more defined regions overlap, the region-defining element
that appears earliest in the document takes precedence (i.e., responds
to user input).
User agents and authors should offer textual alternates to graphical
image maps for cases when graphics are not available or the user
cannot access them. For example, user agents may use alt text to
create textual links in place of a graphical image map. Such links may
be activated in a variety of ways (keyboard, voice activation, etc.).
Note. MAP is not backwards compatible with HTML 2.0 user agents.
Client-side image map examples
In the following example, we create a client-side image map for the
OBJECT element. We do not want to render the image map's contents
when the OBJECT is rendered, so we "hide" the MAP element within the
OBJECT element's content. Consequently, the MAP element's contents
will only be rendered if the OBJECT cannot be rendered.
<HTML>
<HEAD>
<TITLE>The cool site!</TITLE>
</HEAD>
<BODY>
<P><OBJECT data="navbar1.gif" type="image/gif" usemap="#map1">
<MAP name="map1">
<P>Navigate the site:
<A href="guide.html" shape="rect" coords="0,0,118,28">Access Guide</a> |
<A href="shortcut.html" shape="rect" coords="118,0,184,28">Go</A> |
<A href="search.html" shape="circle" coords="184,200,60">Search</A> |
<A href="top10.html" shape="poly" coords="276,0,276,28,100,200,50,50,276
,0">Top Ten</A>
</MAP>
</OBJECT>
</BODY>
</HTML>
We may want to render the image map's contents even when a user agent
can render the OBJECT. For instance, we may want to associate an image
map with an OBJECT element and include a text navigation bar at the
bottom of the page. To do so, we define the MAP element outside the
OBJECT:
<HTML>
<HEAD>
<TITLE>The cool site!</TITLE>
</HEAD>
<BODY>
<P><OBJECT data="navbar1.gif" type="image/gif" usemap="#map1">
</OBJECT>
...the rest of the page here...
<MAP name="map1">
<P>Navigate the site:
<A href="guide.html" shape="rect" coords="0,0,118,28">Access Guide</a> |
<A href="shortcut.html" shape="rect" coords="118,0,184,28">Go</A> |
<A href="search.html" shape="circle" coords="184,200,60">Search</A> |
<A href="top10.html" shape="poly" coords="276,0,276,28,100,200,50,50,276
,0">Top Ten</A>
</MAP>
</BODY>
</HTML>
In the following example, we create a similar image map, this time
using the AREA element. Note the use of alt text:
<P><OBJECT data="navbar1.gif" type="image/gif" usemap="#map1">
<P>This is a navigation bar.
</OBJECT>
<MAP name="map1">
<AREA href="guide.html"
alt="Access Guide"
shape="rect"
coords="0,0,118,28">
<AREA href="search.html"
alt="Search"
shape="rect"
coords="184,0,276,28">
<AREA href="shortcut.html"
alt="Go"
shape="circle"
coords="184,200,60">
<AREA href="top10.html"
alt="Top Ten"
shape="poly"
coords="276,0,276,28,100,200,50,50,276,0">
</MAP>
Here is a similar version using the IMG element instead of OBJECT
(with the same MAP declaration):
<P><IMG src="navbar1.gif" usemap="#map1" alt="navigation bar">
The following example illustrates how image maps may be shared.
Nested OBJECT elements are useful for providing fallbacks in case a
user agent doesn't support certain formats. For example:
<P>
<OBJECT data="navbar.png" type="image/png">
<OBJECT data="navbar.gif" type="image/gif">
text describing the image...
</OBJECT>
</OBJECT>
If the user agent doesn't support the PNG format, it tries to render
the GIF image. If it doesn't support GIF (e.g., it's a speech-based
user agent), it defaults to the text description provided as the
content of the inner OBJECT element. When OBJECT elements are nested
this way, authors may share image maps among them:
<P>
<OBJECT data="navbar.png" type="image/png" usemap="#map1">
<OBJECT data="navbar.gif" type="image/gif" usemap="#map1">
<MAP name="map1">
<P>Navigate the site:
<A href="guide.html" shape="rect" coords="0,0,118,28">Access Guide</a> |
<A href="shortcut.html" shape="rect" coords="118,0,184,28">Go</A> |
<A href="search.html" shape="circle" coords="184,200,60">Search</A> |
<A href="top10.html" shape="poly" coords="276,0,276,28,100,200,50,50,276,
0">Top Ten</A>
</MAP>
</OBJECT>
</OBJECT>
The following example illustrates how anchors may be specified to
create inactive zones within an image map. The first anchor specifies
a small circular region with no associated link. The second anchor
specifies a larger circular region with the same center coordinates.
Combined, the two form a ring whose center is inactive and whose rim
is active. The order of the anchor definitions is important, since the
smaller circle must override the larger circle.
<MAP name="map1">
<P>
<A shape="circle" coords="100,200,50">I'm inactive.</A>
<A href="outer-ring-link.html" shape="circle" coords="100,200,250">I'm active.<
/A>
</MAP>
Similarly, the nohref attribute for the AREA element declares that
geometric region has no associated link.
13.6.2 Server-side image maps
Server-side image maps may be interesting in cases where the image map
is too complicated for a client-side image map.
It is only possible to define a server-side image map for the IMG and
INPUT elements. In the case of IMG, the IMG must be inside an A
element and the boolean attribute ismap ([CI]) must be set. In the
case of INPUT, the INPUT must be of type "image".
When the user activates the link by clicking on the image, the screen
coordinates are sent directly to the server where the document
resides. Screen coordinates are expressed as screen pixel values
relative to the image. For normative information about the definition
of a pixel and how to scale it, please consult [CSS1].
In the following example, the active region defines a server-side
link. Thus, a click anywhere on the image will cause the click's
coordinates to be sent to the server.
<P><A href="http://www.acme.com/cgi-bin/competition">
<IMG src="game.gif" ismap alt="target"></A>
The location clicked is passed to the server as follows. The user
agent derives a new URI from the URI specified by the href attribute
of the A element, by appending `?' followed by the x and y
coordinates, separated by a comma. The link is then followed using the
new URI. For instance, in the given example, if the user clicks at the
location x=10, y=27 then the derived URI is
"http://www.acme.com/cgi-bin/competition?10,27".
User agents that do not offer the user a means to select specific
coordinates (e.g., non-graphical user agents that rely on keyboard
input, speech-based user agents, etc.) should send the coordinates
"0,0" to the server when the link is activated.
13.7 Visual presentation of images, objects, and applets
All IMG and OBJECT attributes that concern visual alignment and
presentation have been deprecated in favor of style sheets.
13.7.1 Width and height
Attribute definitions
width = length [CN]
Image and object width override.
height = length [CN]
Image and object height override.
When specified, the width and height attributes tell user agents to
override the natural image or object size in favor of these values.
When the object is an image, it is scaled. User agents should do their
best to scale an object or image to match the width and height
specified by the author. Note that lengths expressed as percentages
are based on the horizontal or vertical space currently available, not
on the natural size of the image, object, or applet.
The height and width attributes give user agents an idea of the size
of an image or object so that they may reserve space for it and
continue rendering the document while waiting for the image data.
13.7.2 White space around images and objects
Attribute definitions
hspace = pixels [CN]
Deprecated. This attribute specifies the amount of white space
to be inserted to the left and right of an IMG, APPLET, or
OBJECT. The default value is not specified, but is generally a
small, non-zero length.
vspace = pixels [CN]
Deprecated. This attribute specifies the amount of white space
to be inserted above and below an IMG, APPLET, or OBJECT. The
default value is not specified, but is generally a small,
non-zero length.
13.7.3 Borders
An image or object may be surrounded by a border (e.g., when a border
is specified by the user or when the image is the content of an A
element).
Attribute definitions
border = pixels [CN]
Deprecated. This attribute specifies the width of an IMG or
OBJECT border, in pixels. The default value for this attribute
depends on the user agent.
13.7.4 Alignment
Attribute definitions
align = bottom|middle|top|left|right
Deprecated. This attribute specifies the position of an IMG,
OBJECT, or APPLET with respect to its context.
The following values for align concern the object's position with
respect to surrounding text:
* bottom: means that the bottom of the object should be vertically
aligned with the current baseline. This is the default value.
* middle: means that the center of the object should be vertically
aligned with the current baseline.
* top: means that the top of the object should be vertically aligned
with the top of the current text line.
Two other values, left and right, cause the image to float to the
current left or right margin. They are discussed in the section on
floating objects.
Differing interpretations of align. User agents vary in their
interpretation of the align attribute. Some only take into account
what has occurred on the text line prior to the element, some take
into account the text on both sides of the element.
13.8 How to specify alternate text
Attribute definitions
alt = text [CS]
For user agents that cannot display images, forms, or applets,
this attribute specifies alternate text. The language of the
alternate text is specified by the lang attribute.
Several non-textual elements (IMG, AREA, APPLET, and INPUT) let
authors specify alternate text to serve as content when the element
cannot be rendered normally. Specifying alternate text assists users
without graphic display terminals, users whose browsers don't support
forms, visually impaired users, those who use speech synthesizers,
those who have configured their graphical user agents not to display
images, etc.
The alt attribute must be specified for the IMG and AREA elements. It
is optional for the INPUT and APPLET elements.
While alternate text may be very helpful, it must be handled with
care. Authors should observe the following guidelines:
* Do not specify irrelevant alternate text when including images
intended to format a page, for instance, alt="red ball" would be
inappropriate for an image that adds a red ball for decorating a
heading or paragraph. In such cases, the alternate text should be
the empty string (""). Authors are in any case advised to avoid
using images to format pages; style sheets should be used instead.
* Do not specify meaningless alternate text (e.g., "dummy text").
Not only will this frustrate users, it will slow down user agents
that must convert text to speech or braille output.
Implementors should consult the section on accessibility for
information about how to handle cases of omitted alternate text.
14 Style Sheets
Contents
1. Introduction to style sheets
2. Adding style to HTML
1. Setting the default style sheet language
2. Inline style information
3. Header style information: the STYLE element
4. Media types
3. External style sheets
1. Preferred and alternate style sheets
2. Specifying external style sheets
4. Cascading style sheets
1. Media-dependent cascades
2. Inheritance and cascading
5. Hiding style data from user agents
6. Linking to style sheets with HTTP headers
14.1 Introduction to style sheets
Style sheets represent a major breakthrough for Web page designers,
expanding their ability to improve the appearance of their pages. In
the scientific environments in which the Web was conceived, people are
more concerned with the content of their documents than the
presentation. As people from wider walks of life discovered the Web,
the limitations of HTML became a source of continuing frustration and
authors were forced to sidestep HTML's stylistic limitations. While
the intentions have been good -- to improve the presentation of Web
pages -- the techniques for doing so have had unfortunate side
effects. These techniques work for some of the people, some of the
time, but not for all of the people, all of the time. They include:
* Using proprietary HTML extensions
* Converting text into images
* Using images for white space control
* Use of tables for page layout
* Writing a program instead of using HTML
These techniques considerably increase the complexity of Web pages,
offer limited flexibility, suffer from interoperability problems, and
create hardships for people with disabilities.
Style sheets solve these problems at the same time they supersede the
limited range of presentation mechanisms in HTML. Style sheets make it
easy to specify the amount of white space between text lines, the
amount lines are indented, the colors used for the text and the
backgrounds, the font size and style, and a host of other details.
For example, the following short CSS style sheet (stored in the file
"special.css"), sets the text color of a paragraph to green and
surrounds it with a solid red border:
P.special {
color : green;
border: solid red;
}
Authors may link this style sheet to their source HTML document with
the LINK element:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<LINK href="special.css" rel="stylesheet" type="text/css">
</HEAD>
<BODY>
<P class="special">This paragraph should have special green text.
</BODY>
</HTML>
HTML 4 provides support for the following style sheet features:
Flexible placement of style information
Placing style sheets in separate files makes them easy to
reuse. Sometimes it's useful to include rendering instructions
within the document to which they apply, either grouped at the
start of the document, or in attributes of the elements
throughout the body of the document. To make it easier to
manage style on a site basis, this specification describes how
to use HTTP headers to set the style sheets to be applied to a
document.
Independence from specific style sheet languages
This specification doesn't tie HTML to any particular style
sheet language. This allows for a range of such languages to be
used, for instance simple ones for the majority of users and
much more complex ones for the minority of users with highly
specialized needs. The examples included below all use the CSS
(Cascading Style Sheets) language [CSS1], but other style sheet
languages would be possible.
Cascading
This is the capability provided by some style sheet languages
such as CSS to allow style information from several sources to
be blended together. These could be, for instance, corporate
style guidelines, styles common to a group of documents, and
styles specific to a single document. By storing these
separately, style sheets can be reused, simplifying authoring
and making more effective use of network caching. The cascade
defines an ordered sequence of style sheets where rules in
later sheets have greater precedence than earlier ones. Not all
style sheet languages support cascading.
Media dependencies
HTML allows authors to specify documents in a media-independent
way. This allows users to access Web pages using a wide variety
of devices and media, e.g., graphical displays for computers
running Windows, Macintosh OS, and X11, devices for television
sets, specially adapted phones and PDA-based portable devices,
speech-based browsers, and braille-based tactile devices.
Style sheets, by contrast, apply to specific media or media
groups. A style sheet intended for screen use may be applicable
when printing, but is of little use for speech-based browsers.
This specification allows you to define the broad categories of
media a given style sheet is applicable to. This allows user
agents to avoid retrieving inappropriate style sheets. Style
sheet languages may include features for describing media
dependencies within the same style sheet.
Alternate styles
Authors may wish to offer readers several ways to view a
document. For instance, a style sheet for rendering compact
documents with small fonts, or one that specifies larger fonts
for increased legibility. This specification allows authors to
specify a preferred style sheet as well as alternates that
target specific users or media. User agents should give users
the opportunity to select from among alternate style sheets or
to switch off style sheets altogether.
Performance concerns
Some people have voiced concerns over performance issues for
style sheets. For instance, retrieving an external style sheet
may delay the full presentation for the user. A similar
situation arises if the document head includes a lengthy set of
style rules.
The current proposal addresses these issues by allowing authors
to include rendering instructions within each HTML element. The
rendering information is then always available by the time the
user agent wants to render each element.
In many cases, authors will take advantage of a common style
sheet for a group of documents. In this case, distributing
style rules throughout the document will actually lead to worse
performance than using a linked style sheet, since for most
documents, the style sheet will already be present in the local
cache. The public availability of good style sheets will
encourage this effect.
14.2 Adding style to HTML
Note. The sample default style sheet for HTML 4 that is included in
[CSS2] expresses generally accepted default style information for
each element. Authors and implementors alike might find this a useful
resource.
HTML documents may contain style sheet rules directly in them or they
may import style sheets.
Any style sheet language may be used with HTML. A simple style sheet
language may suffice for the needs of most users, but other languages
may be more suited to highly specialized needs. This specification
uses the style language "Cascading Style Sheets" ([CSS1]), abbreviated
CSS, for examples.
The syntax of style data depends on the style sheet language.
14.2.1 Setting the default style sheet language
Authors must specify the style sheet language of style information
associated with an HTML document.
Authors should use the META element to set the default style sheet
language for a document. For example, to set the default to CSS,
authors should put the following declaration in the HEAD of their
documents:
<META http-equiv="Content-Style-Type" content="text/css">
The default style sheet language may also be set with HTTP headers.
The above META declaration is equivalent to the HTTP header:
Content-Style-Type: text/css
User agents should determine the default style sheet language for a
document according to the following steps (highest to lowest
priority):
1. If any META declarations specify the "Content-Style-Type", the
last one in the character stream determines the default style
sheet language.
2. Otherwise, if any HTTP headers specify the "Content-Style-Type",
the last one in the character stream determines the default style
sheet language.
3. Otherwise, the default style sheet language is "text/css".
Documents that include elements that set the style attribute but which
don't define a default style sheet language are incorrect. Authoring
tools should generate default style sheet language information
(typically a META declaration) so that user agents do not have to rely
on a default of "text/css".
14.2.2 Inline style information
Attribute definitions
style = style [CN]
This attribute specifies style information for the current
element.
The syntax of the value of the style attribute is determined by the
default style sheet language. For example, for [[CSS2]] inline style,
use the declaration block syntax described in section 4.1.8 (without
curly brace delimiters).
This CSS example sets color and font size information for the text in
a specific paragraph.
<P style="font-size: 12pt; color: fuchsia">Aren't style sheets wonderful?
In CSS, property declarations have the form "name : value" and are
separated by a semi-colon.
To specify style information for more than one element, authors should
use the STYLE element. For optimal flexibility, authors should define
styles in external style sheets.
14.2.3 Header style information: the STYLE element
<!ELEMENT STYLE - - %StyleSheet -- style info -->
<!ATTLIST STYLE
%i18n; -- lang, dir, for use with title --
type %ContentType; #REQUIRED -- content type of style language --
media %MediaDesc; #IMPLIED -- designed for use with these media --
title %Text; #IMPLIED -- advisory title --
>
Start tag: required, End tag: required
Attribute definitions
type = content-type [CI]
This attribute specifies the style sheet language of the
element's contents and overrides the default style sheet
language. The style sheet language is specified as a content
type (e.g., "text/css"). Authors must supply a value for this
attribute; there is no default value for this attribute.
media = media-descriptors [CI]
This attribute specifies the intended destination medium for
style information. It may be a single media descriptor or a
comma-separated list. The default value for this attribute is
"screen".
Attributes defined elsewhere
* lang (language information), dir (text direction)
* title (element title)
The STYLE element allows authors to put style sheet rules in the head
of the document. HTML permits any number of STYLE elements in the HEAD
section of a document.
User agents that don't support style sheets, or don't support the
specific style sheet language used by a STYLE element, must hide the
contents of the STYLE element. It is an error to render the content as
part of the document's text. Some style sheet languages support syntax
for hiding the content from non-conforming user agents.
The syntax of style data depends on the style sheet language.
Some style sheet implementations may allow a wider variety of rules in
the STYLE element than in the style attribute. For example, with CSS,
rules may be declared within a STYLE element for:
* All instances of a specific HTML element (e.g., all P elements,
all H1 elements, etc.)
* All instances of an HTML element belonging to a specific class
(i.e., whose class attribute is set to some value).
* Single instances of an HTML element (i.e., whose id attribute is
set to some value).
Rules for style rule precedences and inheritance depend on the style
sheet language.
The following CSS STYLE declaration puts a border around every H1
element in the document and centers it on the page.
<HEAD>
<STYLE type="text/css">
H1 {border-width: 1; border: solid; text-align: center}
</STYLE>
</HEAD>
To specify that this style information should only apply to H1
elements of a specific class, we modify it as follows:
<HEAD>
<STYLE type="text/css">
H1.myclass {border-width: 1; border: solid; text-align: center}
</STYLE>
</HEAD>
<BODY>
<H1 class="myclass"> This H1 is affected by our style </H1>
<H1> This one is not affected by our style </H1>
</BODY>
Finally, to limit the scope of the style information to a single
instance of H1, set the id attribute:
<HEAD>
<STYLE type="text/css">
#myid {border-width: 1; border: solid; text-align: center}
</STYLE>
</HEAD>
<BODY>
<H1 class="myclass"> This H1 is not affected </H1>
<H1 id="myid"> This H1 is affected by style </H1>
<H1> This H1 is not affected </H1>
</BODY>
Although style information may be set for almost every HTML element,
two elements, DIV and SPAN, are particularly useful in that they do
not impose any presentation semantics (besides block-level vs.
inline). When combined with style sheets, these elements allow users
to extend HTML indefinitely, particularly when used with the class and
id attributes.
In the following example, we use the SPAN element to set the font
style of the first few words of a paragraph to small caps.
<HEAD>
<STYLE type="text/css">
SPAN.sc-ex { font-variant: small-caps }
</STYLE>
</HEAD>
<BODY>
<P><SPAN class="sc-ex">The first</SPAN> few words of
this paragraph are in small-caps.
</BODY>
In the following example, we use DIV and the class attribute to set
the text justification for a series of paragraphs that make up the
abstract section of a scientific article. This style information could
be reused for other abstract sections by setting the class attribute
elsewhere in the document.
<HEAD>
<STYLE type="text/css">
DIV.Abstract { text-align: justify }
</STYLE>
</HEAD>
<BODY>
<DIV class="Abstract">
<P>The Chieftain product range is our market winner for
the coming year. This report sets out how to position
Chieftain against competing products.
<P>Chieftain replaces the Commander range, which will
remain on the price list until further notice.
</DIV>
</BODY>
14.2.4 Media types
HTML allows authors to design documents that take advantage of the
characteristics of the media where the document is to be rendered
(e.g., graphical displays, television screens, handheld devices,
speech-based browsers, braille-based tactile devices, etc.). By
specifying the media attribute, authors allow user agents to load and
apply style sheets selectively. Please consult the list of recognized
media descriptors.
The following sample declarations apply to H1 elements. When projected
in a business meeting, all instances will be blue. When printed, all
instances will be centered.
<HEAD>
<STYLE type="text/css" media="projection">
H1 { color: blue}
</STYLE>
<STYLE type="text/css" media="print">
H1 { text-align: center }
</STYLE>
This example adds sound effects to anchors for use in speech output:
<STYLE type="text/css" media="aural">
A { cue-before: uri(bell.aiff); cue-after: uri(dong.wav)}
</STYLE>
</HEAD>
Media control is particularly interesting when applied to external
style sheets since user agents can save time by retrieving from the
network only those style sheets that apply to the current device. For
instance, speech-based browsers can avoid downloading style sheets
designed for visual rendering. See the section on media-dependent
cascades for more information.
14.3 External style sheets
Authors may separate style sheets from HTML documents. This offers
several benefits:
* Authors and Web site managers may share style sheets across a
number of documents (and sites).
* Authors may change the style sheet without requiring modifications
to the document.
* User agents may load style sheets selectively (based on media
descriptions).
14.3.1 Preferred and alternate style sheets
HTML allows authors to associate any number of external style sheets
with a document. The style sheet language defines how multiple
external style sheets interact (for example, the CSS "cascade" rules).
Authors may specify a number of mutually exclusive style sheets called
alternate style sheets. Users may select their favorite among these
depending on their preferences. For instance, an author may specify
one style sheet designed for small screens and another for users with
weak vision (e.g., large fonts). User agents should allow users to
select from alternate style sheets.
The author may specify that one of the alternates is a preferred style
sheet. User agents should apply the author's preferred style sheet
unless the user has selected a different alternate.
Authors may group several alternate style sheets (including the
author's preferred style sheets) under a single style name. When a
user selects a named style, the user agent must apply all style sheets
with that name. User agents must not apply alternate style sheets with
a different style name. The section on specifying external style
sheets explains how to name a group of style sheets.
Authors may also specify persistent style sheets that user agents must
apply in addition to any alternate style sheet.
User agents must respect media descriptors when applying any style
sheet.
User agents should also allow users to disable the author's style
sheets entirely, in which case the user agent must not apply any
persistent or alternate style sheets.
14.3.2 Specifying external style sheets
Authors specify external style sheets with the following attributes of
the LINK element:
* Set the value of href to the location of the style sheet file. The
value of href is a URI.
* Set the value of the type attribute to indicate the language of
the linked (style sheet) resource. This allows the user agent to
avoid downloading a style sheet for an unsupported style sheet
language.
* Specify that the style sheet is persistent, preferred, or
alternate:
+ To make a style sheet persistent, set the rel attribute to
"stylesheet" and don't set the title attribute.
+ To make a style sheet preferred, set the rel attribute to
"stylesheet" and name the style sheet with the title
attribute.
+ To specify an alternate style sheet, set the rel attribute to
"alternate stylesheet" and name the style sheet with the
title attribute.
User agents should provide a means for users to view and pick from the
list of alternate styles. The value of the title attribute is
recommended as the name of each choice.
In this example, we first specify a persistent style sheet located in
the file mystyle.css:
<LINK href="mystyle.css" rel="stylesheet" type="text/css">
Setting the title attribute makes this the author's preferred style
sheet:
<LINK href="mystyle.css" title="compact" rel="stylesheet" type="text/css">
Adding the keyword "alternate" to the rel attribute makes it an
alternate style sheet:
<LINK href="mystyle.css" title="Medium" rel="alternate stylesheet" type="text/c
ss">
For more information on external style sheets, please consult the
section on links and external style sheets.
Authors may also use the META element to set the document's preferred
style sheet. For example, to set the preferred style sheet to
"compact" (see the preceding example), authors may include the
following line in the HEAD:
<META http-equiv="Default-Style" content="compact">
The preferred style sheet may also be specified with HTTP headers. The
above META declaration is equivalent to the HTTP header:
Default-Style: "compact"
If two or more META declarations or HTTP headers specify the preferred
style sheet, the last one takes precedence. HTTP headers are
considered to occur earlier than the document HEAD for this purpose.
If two or more LINK elements specify a preferred style sheet, the
first one takes precedence.
Preferred style sheets specified with META or HTTP headers have
precedence over those specified with the LINK element.
14.4 Cascading style sheets
Cascading style sheet languages such as CSS allow style information
from several sources to be blended together. However, not all style
sheet languages support cascading. To define a cascade, authors
specify a sequence of LINK and/or STYLE elements. The style
information is cascaded in the order the elements appear in the HEAD.
Note. This specification does not specify how style sheets from
different style languages cascade. Authors should avoid mixing style
sheet languages.
In the following example, we specify two alternate style sheets named
"compact". If the user selects the "compact" style, the user agent
must apply both external style sheets, as well as the persistent
"common.css" style sheet. If the user selects the "big print" style,
only the alternate style sheet "bigprint.css" and the persistent
"common.css" will be applied.
<LINK rel="alternate stylesheet" title="compact" href="small-base.css" type="te
xt/css">
<LINK rel="alternate stylesheet" title="compact" href="small-extras.css" type="
text/css">
<LINK rel="alternate stylesheet" title="big print" href="bigprint.css" type="te
xt/css">
<LINK rel="stylesheet" href="common.css" type="text/css">
Here is a cascade example that involves both the LINK and STYLE
elements.
<LINK rel="stylesheet" href="corporate.css" type="text/css">
<LINK rel="stylesheet" href="techreport.css" type="text/css">
<STYLE type="text/css">
p.special { color: rgb(230, 100, 180) }
</STYLE>
14.4.1 Media-dependent cascades
A cascade may include style sheets applicable to different media. Both
LINK and STYLE may be used with the media attribute. The user agent is
then responsible for filtering out those style sheets that do not
apply to the current medium.
In the following example, we define a cascade where the "corporate"
style sheet is provided in several versions: one suited to printing,
one for screen use and one for speech-based browsers (useful, say,
when reading email in the car). The "techreport" stylesheet applies to
all media. The color rule defined by the STYLE element is used for
print and screen but not for aural rendering.
<LINK rel="stylesheet" media="aural" href="corporate-aural.css" type="text/css"
>
<LINK rel="stylesheet" media="screen" href="corporate-screen.css" type="text/cs
s">
<LINK rel="stylesheet" media="print" href="corporate-print.css" type="text/css"
>
<LINK rel="stylesheet" href="techreport.css" type="text/css">
<STYLE media="screen, print" type="text/css">
p.special { color: rgb(230, 100, 180) }
</STYLE>
14.4.2 Inheritance and cascading
When the user agent wants to render a document, it needs to find
values for style properties, e.g. the font family, font style, size,
line height, text color and so on. The exact mechanism depends on the
style sheet language, but the following description is generally
applicable:
The cascading mechanism is used when a number of style rules all apply
directly to an element. The mechanism allows the user agent to sort
the rules by specificity, to determine which rule to apply. If no rule
can be found, the next step depends on whether the style property can
be inherited or not. Not all properties can be inherited. For these
properties the style sheet language provides default values for use
when there are no explicit rules for a particular element.
If the property can be inherited, the user agent examines the
immediately enclosing element to see if a rule applies to that. This
process continues until an applicable rule is found. This mechanism
allows style sheets to be specified compactly. For instance, authors
may specify the font family for all elements within the BODY by a
single rule that applies to the BODY element.
14.5 Hiding style data from user agents
Some style sheet languages support syntax intended to allow authors to
hide the content of STYLE elements from non-conforming user agents.
This example illustrates for CSS how to comment out the content of
STYLE elements to ensure that older, non-conforming user agents will
not render them as text.
<STYLE type="text/css">
<!--
H1 { color: red }
P { color: blue}
-->
</STYLE>
14.6 Linking to style sheets with HTTP headers
This section only applies to user agents conforming to versions of
HTTP that define a Link header field. Note that HTTP 1.1 as defined by
[RFC2616] does not include a Link header field (refer to section
19.6.3).
Web server managers may find it convenient to configure a server so
that a style sheet will be applied to a group of pages. The HTTP Link
header has the same effect as a LINK element with the same attributes
and values. Multiple Link headers correspond to multiple LINK elements
occurring in the same order. For instance,
Link: <http://www.acme.com/corporate.css>; REL=stylesheet
corresponds to:
<LINK rel="stylesheet" href="http://www.acme.com/corporate.css">
It is possible to specify several alternate styles using multiple Link
headers, and then use the rel attribute to determine the default
style.
In the following example, "compact" is applied by default since it
omits the "alternate" keyword for the rel attribute.
Link: <compact.css>; rel="stylesheet"; title="compact"
Link: <bigprint.css>; rel="alternate stylesheet"; title="big print"
This should also work when HTML documents are sent by email. Some
email agents can alter the ordering of [RFC822] headers. To protect
against this affecting the cascading order for style sheets specified
by Link headers, authors can use header concatenation to merge several
instances of the same header field. The quote marks are only needed
when the attribute values include whitespace. Use SGML entities to
reference characters that are otherwise not permitted within HTTP or
email headers, or that are likely to be affected by transit through
gateways.
LINK and META elements implied by HTTP headers are defined as
occurring before any explicit LINK and META elements in the document's
HEAD.
15 Alignment, font styles, and horizontal rules
Contents
1. Formatting
1. Background color
2. Alignment
3. Floating objects
o Float an object
o Float text around an object
2. Fonts
1. Font style elements: the TT, I, B, BIG, SMALL, STRIKE, S, and
U elements
2. Font modifier elements: FONT and BASEFONT
3. Rules: the HR element
This section of the specification discusses some HTML elements and
attributes that may be used for visual formatting of elements. Many of
them are deprecated.
15.1 Formatting
15.1.1 Background color
Attribute definitions
bgcolor = color [CI]
Deprecated. This attribute sets the background color for the
document body or table cells.
This attribute sets the background color of the canvas for the
document body (the BODY element) or for tables (the TABLE, TR, TH, and
TD elements). Additional attributes for specifying text color can be
used with the BODY element.
This attribute has been deprecated in favor of style sheets for
specifying background color information.
15.1.2 Alignment
It is possible to align block elements (tables, images, objects,
paragraphs, etc.) on the canvas with the align attribute. Although
this attribute may be set for many HTML elements, its range of
possible values sometimes differs from element to element. Here we
only discuss the meaning of the align attribute for text.
Attribute definitions
align = left|center|right|justify [CI]
Deprecated. This attribute specifies the horizontal alignment
of its element with respect to the surrounding context.
Possible values:
+ left: text lines are rendered flush left.
+ center: text lines are centered.
+ right: text lines are rendered flush right.
+ justify: text lines are justified to both margins.
The default depends on the base text direction. For left to right
text, the default is align=left, while for right to left text, the
default is align=right.
DEPRECATED EXAMPLE:
This example centers a heading on the canvas.
<H1 align="center"> How to Carve Wood </H1>
Using CSS, for example, you could achieve the same effect as follows:
<HEAD>
<TITLE>How to Carve Wood</TITLE>
<STYLE type="text/css">
H1 { text-align: center}
</STYLE>
<BODY>
<H1> How to Carve Wood </H1>
Note that this would center all H1 declarations. You could reduce the
scope of the style by setting the class attribute on the element:
<HEAD>
<TITLE>How to Carve Wood</TITLE>
<STYLE type="text/css">
H1.wood {text-align: center}
</STYLE>
<BODY>
<H1 class="wood"> How to Carve Wood </H1>
DEPRECATED EXAMPLE:
Similarly, to right align a paragraph on the canvas with HTML's align
attribute you could have:
<P align="right">...Lots of paragraph text...
which, with CSS, would be:
<HEAD>
<TITLE>How to Carve Wood</TITLE>
<STYLE type="text/css">
P.mypar {text-align: right}
</STYLE>
<BODY>
<P class="mypar">...Lots of paragraph text...
DEPRECATED EXAMPLE:
To right align a series of paragraphs, group them with the DIV
element:
<DIV align="right">
<P>...text in first paragraph...
<P>...text in second paragraph...
<P>...text in third paragraph...
</DIV>
With CSS, the text-align property is inherited from the parent
element, you can therefore use:
<HEAD>
<TITLE>How to Carve Wood</TITLE>
<STYLE type="text/css">
DIV.mypars {text-align: right}
</STYLE>
<BODY>
<DIV class="mypars">
<P>...text in first paragraph...
<P>...text in second paragraph...
<P>...text in third paragraph...
</DIV>
To center the entire document with CSS:
<HEAD>
<TITLE>How to Carve Wood</TITLE>
<STYLE type="text/css">
BODY {text-align: center}
</STYLE>
<BODY>
...the body is centered...
</BODY>
The CENTER element is exactly equivalent to specifying the DIV element
with the align attribute set to "center". The CENTER element is
deprecated.
15.1.3 Floating objects
Images and objects may appear directly "in-line" or may be floated to
one side of the page, temporarily altering the margins of text that
may flow on either side of the object.
Float an object
The align attribute for objects, images, tables, frames, etc., causes
the object to float to the left or right margin. Floating objects
generally begin a new line. This attribute takes the following values:
* left: Floats the object to the current left margin. Subsequent
text flows along the image's right side.
* right: Floats the object to the current right margin. Subsequent
text flows along the image's left side.
DEPRECATED EXAMPLE:
The following example shows how to float an IMG element to the current
left margin of the canvas.
<IMG align="left" src="http://foo.com/animage.gif" alt="my boat">
Some alignment attributes also permit the "center" value, which does
not cause floating, but centers the object within the current margins.
However, for P and DIV, the value "center" causes the contents of the
element to be centered.
Float text around an object
Another attribute, defined for the BR element, controls text flow
around floating objects.
Attribute definitions
clear = none|left|right|all [CI]
Deprecated. Specifies where the next line should appear in a
visual browser after the line break caused by this element.
This attribute takes into account floating objects (images,
tables, etc.). Possible values:
+ none: The next line will begin normally. This is the default
value.
+ left: The next line will begin at nearest line below any
floating objects on the left-hand margin.
+ right: The next line will begin at nearest line below any
floating objects on the right-hand margin.
+ all: The next line will begin at nearest line below any
floating objects on either margin.
Consider the following visual scenario, where text flows to the right
of an image until a line is broken by a BR:
********* -------
| | -------
| image | --<BR>
| |
*********
If the clear attribute is set to none, the line following BR will
begin immediately below it at the right margin of the image:
********* -------
| | -------
| image | --<BR>
| | ------
*********
DEPRECATED EXAMPLE:
If the clear attribute is set to left or all, the next line will
appear as follows:
********* -------
| | -------
| image | --<BR clear="left">
| |
*********
-----------------
Using style sheets, you could specify that all line breaks should
behave this way for objects (images, tables, etc.) floating against
the left margin. With CSS, you could achieve this as follows:
<STYLE type="text/css">
BR { clear: left }
</STYLE>
To specify this behavior for a specific instance of the BR element,
you could combine style information and the id attribute:
<HEAD>
...
<STYLE type="text/css">
BR#mybr { clear: left }
</STYLE>
</HEAD>
<BODY>
<P>...
********* -------
| | -------
| table | --<BR id="mybr">
| |
*********
-----------------
...
</BODY>
15.2 Fonts
The following HTML elements specify font information. Although they
are not all deprecated, their use is discouraged in favor of style
sheets.
15.2.1 Font style elements: the TT, I, B, BIG, SMALL, STRIKE, S, and U
elements
<!ENTITY % fontstyle
"TT | I | B | BIG | SMALL">
<!ELEMENT (%fontstyle;|%phrase;) - - (%inline;)*>
<!ATTLIST (%fontstyle;|%phrase;)
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: required
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown onkeyup (intrinsic
events)
Rendering of font style elements depends on the user agent. The
following is an informative description only.
TT: Renders as teletype or monospaced text.
I: Renders as italic text style.
B: Renders as bold text style.
BIG: Renders text in a "large" font.
SMALL: Renders text in a "small" font.
STRIKE and S: Deprecated. Render strike-through style text.
U: Deprecated. Renders underlined text.
The following sentence shows several types of text:
<P><b>bold</b>,
<i>italic</i>, <b><i>bold italic</i></b>, <tt>teletype text</tt>, and
<big>big</big> and <small>small</small> text.
These words might be rendered as follows:
An example of rendering of various font styles
It is possible to achieve a much richer variety of font effects using
style sheets. To specify blue, italic text in a paragraph with CSS:
<HEAD>
<STYLE type="text/css">
P#mypar {font-style: italic; color: blue}
</STYLE>
</HEAD>
<P id="mypar">...Lots of blue italic text...
Font style elements must be properly nested. Rendering of nested font
style elements depends on the user agent.
15.2.2 Font modifier elements: FONT and BASEFONT
FONT and BASEFONT are deprecated.
See the Transitional DTD for the formal definition.
Attribute definitions
size = cdata [CN]
Deprecated. This attribute sets the size of the font. Possible
values:
+ An integer between 1 and 7. This sets the font to some fixed
size, whose rendering depends on the user agent. Not all user
agents may render all seven sizes.
+ A relative increase in font size. The value "+1" means one
size larger. The value "-3" means three sizes smaller. All
sizes belong to the scale of 1 to 7.
color = color [CI]
Deprecated. This attribute sets the text color.
face = cdata [CI]
Deprecated. This attribute defines a comma-separated list of
font names the user agent should search for in order of
preference.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
The FONT element changes the font size and color for text in its
contents.
The BASEFONT element sets the base font size (using the size
attribute). Font size changes achieved with FONT are relative to the
base font size set by BASEFONT. If BASEFONT is not used, the default
base font size is 3.
DEPRECATED EXAMPLE:
The following example will show the difference between the seven font
sizes available with FONT:
<P><font size=1>size=1</font>
<font size=2>size=2</font>
<font size=3>size=3</font>
<font size=4>size=4</font>
<font size=5>size=5</font>
<font size=6>size=6</font>
<font size=7>size=7</font>
This might be rendered as:
Example of rendering of various font sizes
The following shows an example of the effect of relative font sizes
using a base font size of 3:
Example of rendering of various font sizes with a basefont
The base font size does not apply to headings, except where these are
modified using the FONT element with a relative font size change.
15.3 Rules: the HR element
<!ELEMENT HR - O EMPTY -- horizontal rule -->
<!ATTLIST HR
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: forbidden
Attribute definitions
align = left|center|right [CI]
Deprecated. This attribute specifies the horizontal alignment
of the rule with respect to the surrounding context. Possible
values:
+ left: the rule is rendered flush left.
+ center: the rule is centered.
+ right: the rule is rendered flush right.
The default is align=center.
noshade [CI]
Deprecated. When set, this boolean attribute requests that the
user agent render the rule in a solid color rather than as the
traditional two-color "groove".
size = pixels [CI]
Deprecated. This attribute specifies the height of the rule.
The default value for this attribute depends on the user agent.
width = length [CI]
Deprecated. This attribute specifies the width of the rule. The
default width is 100%, i.e., the rule extends across the entire
canvas.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
The HR element causes a horizontal rule to be rendered by visual user
agents.
The amount of vertical space inserted between a rule and the content
that surrounds it depends on the user agent.
DEPRECATED EXAMPLE:
This example centers the rules, sizing them to half the available
width between the margins. The top rule has the default thickness
while the bottom two are set to 5 pixels. The bottom rule should be
rendered in a solid color without shading:
<HR width="50%" align="center">
<HR size="5" width="50%" align="center">
<HR noshade size="5" width="50%" align="center">
These rules might be rendered as follows:
Example of rendering of various horizontal rules
16 Frames
Contents
1. Introduction to frames
2. Layout of frames
1. The FRAMESET element
o Rows and columns
o Nested frame sets
o Sharing data among frames
2. The FRAME element
o Setting the initial contents of a frame
o Visual rendering of a frame
3. Specifying target frame information
1. Setting the default target for links
2. Target semantics
4. Alternate content
1. The NOFRAMES element
2. Long descriptions of frames
5. Inline frames: the IFRAME element
16.1 Introduction to frames
HTML frames allow authors to present documents in multiple views,
which may be independent windows or subwindows. Multiple views offer
designers a way to keep certain information visible, while other views
are scrolled or replaced. For example, within the same window, one
frame might display a static banner, a second a navigation menu, and a
third the main document that can be scrolled through or replaced by
navigating in the second frame.
Here is a simple frame document:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A simple frameset document</TITLE>
</HEAD>
<FRAMESET cols="20%, 80%">
<FRAMESET rows="100, 200">
<FRAME src="contents_of_frame1.html">
<FRAME src="contents_of_frame2.gif">
</FRAMESET>
<FRAME src="contents_of_frame3.html">
<NOFRAMES>
<P>This frameset document contains:
<UL>
<LI><A href="contents_of_frame1.html">Some neat contents</A>
<LI><IMG src="contents_of_frame2.gif" alt="A neat image">
<LI><A href="contents_of_frame3.html">Some other neat contents</A>
</UL>
</NOFRAMES>
</FRAMESET>
</HTML>
that might create a frame layout something like this:
---------------------------------------
| | |
| | |
| Frame 1 | |
| | |
| | |
|---------| |
| | Frame 3 |
| | |
| | |
| | |
| Frame 2 | |
| | |
| | |
| | |
| | |
---------------------------------------
If the user agent can't display frames or is configured not to, it
will render the contents of the NOFRAMES element.
16.2 Layout of frames
An HTML document that describes frame layout (called a frameset
document) has a different makeup than an HTML document without frames.
A standard document has one HEAD section and one BODY. A frameset
document has a HEAD, and a FRAMESET in place of the BODY.
The FRAMESET section of a document specifies the layout of views in
the main user agent window. In addition, the FRAMESET section can
contain a NOFRAMES element to provide alternate content for user
agents that do not support frames or are configured not to display
frames.
Elements that might normally be placed in the BODY element must not
appear before the first FRAMESET element or the FRAMESET will be
ignored.
16.2.1 The FRAMESET element
<![ %HTML.Frameset; [
<!ELEMENT FRAMESET - - ((FRAMESET|FRAME)+ & NOFRAMES?) -- window subdivision-->
<!ATTLIST FRAMESET
%coreattrs; -- id, class, style, title --
rows %MultiLengths; #IMPLIED -- list of lengths,
default: 100% (1 row) --
cols %MultiLengths; #IMPLIED -- list of lengths,
default: 100% (1 col) --
onload %Script; #IMPLIED -- all the frames have been loaded --
onunload %Script; #IMPLIED -- all the frames have been removed --
>
]]>
Attribute definitions
rows = multi-length-list [CN]
This attribute specifies the layout of horizontal frames. It is
a comma-separated list of pixels, percentages, and relative
lengths. The default value is 100%, meaning one row.
cols = multi-length-list [CN]
This attribute specifies the layout of vertical frames. It is a
comma-separated list of pixels, percentages, and relative
lengths. The default value is 100%, meaning one column.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* title (element title)
* style (inline style information)
* onload, onunload (intrinsic events)
The FRAMESET element specifies the layout of the main user window in
terms of rectangular subspaces.
Rows and columns
Setting the rows attribute defines the number of horizontal subspaces
in a frameset. Setting the cols attribute defines the number of
vertical subspaces. Both attributes may be set simultaneously to
create a grid.
If the rows attribute is not set, each column extends the entire
length of the page. If the cols attribute is not set, each row extends
the entire width of the page. If neither attribute is set, the frame
takes up exactly the size of the page.
Frames are created left-to-right for columns and top-to-bottom for
rows. When both attributes are specified, views are created
left-to-right in the top row, left-to-right in the second row, etc.
The first example divides the screen vertically in two (i.e., creates
a top half and a bottom half).
<FRAMESET rows="50%, 50%">
...the rest of the definition...
</FRAMESET>
The next example creates three columns: the second has a fixed width
of 250 pixels (useful, for example, to hold an image with a known
size). The first receives 25% of the remaining space and the third 75%
of the remaining space.
<FRAMESET cols="1*,250,3*">
...the rest of the definition...
</FRAMESET>
The next example creates a 2x3 grid of subspaces.
<FRAMESET rows="30%,70%" cols="33%,34%,33%">
...the rest of the definition...
</FRAMESET>
For the next example, suppose the browser window is currently 1000
pixels high. The first view is allotted 30% of the total height (300
pixels). The second view is specified to be exactly 400 pixels high.
This leaves 300 pixels to be divided between the other two frames. The
fourth frame's height is specified as "2*", so it is twice as high as
the third frame, whose height is only "*" (equivalent to 1*).
Therefore the third frame will be 100 pixels high and the fourth will
be 200 pixels high.
<FRAMESET rows="30%,400,*,2*">
...the rest of the definition...
</FRAMESET>
Absolute lengths that do not sum to 100% of the real available space
should be adjusted by the user agent. When underspecified, remaining
space should be allotted proportionally to each view. When
overspecified, each view should be reduced according to its specified
proportion of the total space.
Nested frame sets
Framesets may be nested to any level.
In the following example, the outer FRAMESET divides the available
space into three equal columns. The inner FRAMESET then divides the
second area into two rows of unequal height.
<FRAMESET cols="33%, 33%, 34%">
...contents of first frame...
<FRAMESET rows="40%, 50%">
...contents of second frame, first row...
...contents of second frame, second row...
</FRAMESET>
...contents of third frame...
</FRAMESET>
Sharing data among frames
Authors may share data among several frames by including this data via
an OBJECT element. Authors should include the OBJECT element in the
HEAD element of a frameset document and name it with the id
attribute. Any document that is the contents of a frame in the
frameset may refer to this identifier.
The following example illustrates how a script might refer to an
OBJECT element defined for an entire frameset:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>This is a frameset with OBJECT in the HEAD</TITLE>
<!-- This OBJECT is not rendered! -->
<OBJECT id="myobject" data="data.bar"></OBJECT>
</HEAD>
<FRAMESET>
<FRAME src="bianca.html" name="bianca">
</FRAMESET>
</HTML>
<!-- In bianca.html -->
<HTML>
<HEAD>
<TITLE>Bianca's page</TITLE>
</HEAD>
<BODY>
...the beginning of the document...
<P>
<SCRIPT type="text/javascript">
parent.myobject.myproperty
</SCRIPT>
...the rest of the document...
</BODY>
</HTML>
16.2.2 The FRAME element
<![ %HTML.Frameset; [
<!-- reserved frame names start with "_" otherwise starts with letter -->
<!ELEMENT FRAME - O EMPTY -- subwindow -->
<!ATTLIST FRAME
%coreattrs; -- id, class, style, title --
longdesc %URI; #IMPLIED -- link to long description
(complements title) --
name CDATA #IMPLIED -- name of frame for targetting --
src %URI; #IMPLIED -- source of frame content --
frameborder (1|0) 1 -- request frame borders? --
marginwidth %Pixels; #IMPLIED -- margin widths in pixels --
marginheight %Pixels; #IMPLIED -- margin height in pixels --
noresize (noresize) #IMPLIED -- allow users to resize frames? --
scrolling (yes|no|auto) auto -- scrollbar or none --
>
]]>
Attribute definitions
name = cdata [CI]
This attribute assigns a name to the current frame. This name
may be used as the target of subsequent links.
longdesc = uri [CT]
This attribute specifies a link to a long description of the
frame. This description should supplement the short description
provided using the title attribute, and may be particularly
useful for non-visual user agents.
src = uri [CT]
This attribute specifies the location of the initial contents
to be contained in the frame.
noresize [CI]
When present, this boolean attribute tells the user agent that
the frame window must not be resizeable.
scrolling = auto|yes|no [CI]
This attribute specifies scroll information for the frame
window. Possible values
+ auto: This value tells the user agent to provide scrolling
devices for the frame window when necessary. This is the
default value.
+ yes: This value tells the user agent to always provide
scrolling devices for the frame window.
+ no: This value tells the user agent not to provide scrolling
devices for the frame window.
frameborder = 1|0 [CN]
This attribute provides the user agent with information about
the frame border. Possible values:
+ 1: This value tells the user agent to draw a separator
between this frame and every adjoining frame. This is the
default value.
+ 0: This value tells the user agent not to draw a separator
between this frame and every adjoining frame. Note that
separators may be drawn next to this frame nonetheless if
specified by other frames.
marginwidth = pixels [CN]
This attribute specifies the amount of space to be left between
the frame's contents in its left and right margins. The value
must be greater than zero (pixels). The default value depends
on the user agent.
marginheight = pixels [CN]
This attribute specifies the amount of space to be left between
the frame's contents in its top and bottom margins. The value
must be greater than zero (pixels). The default value depends
on the user agent.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* title (element title)
* style (inline style information)
The FRAME element defines the contents and appearance of a single
frame.
Setting the initial contents of a frame
The src attribute specifies the initial document the frame will
contain.
The following example HTML document:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A frameset document</TITLE>
</HEAD>
<FRAMESET cols="33%,33%,33%">
<FRAMESET rows="*,200">
<FRAME src="contents_of_frame1.html">
<FRAME src="contents_of_frame2.gif">
</FRAMESET>
<FRAME src="contents_of_frame3.html">
<FRAME src="contents_of_frame4.html">
</FRAMESET>
</HTML>
should create a frame layout something like this:
------------------------------------------
|Frame 1 |Frame 3 |Frame 4 |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
-------------| | |
|Frame 2 | | |
| | | |
| | | |
------------------------------------------
and cause the user agent to load each file into a separate view.
The contents of a frame must not be in the same document as the
frame's definition.
ILLEGAL EXAMPLE:
The following frameset definition is not legal HTML since the contents
of the second frame are in the same document as the frameset.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A frameset document</TITLE>
</HEAD>
<FRAMESET cols="50%,50%">
<FRAME src="contents_of_frame1.html">
<FRAME src="#anchor_in_same_document">
<NOFRAMES>
...some text...
<H2><A name="anchor_in_same_document">Important section</A></H2>
...some text...
</NOFRAMES>
</FRAMESET>
</HTML>
Visual rendering of a frame
The following example illustrates the usage of the decorative FRAME
attributes. We specify that frame 1 will allow no scroll bars. Frame 2
will leave white space around its contents (initially, an image file)
and the frame will not be resizeable. No border will be drawn between
frames 3 and 4. Borders will be drawn (by default) between frames 1,
2, and 3.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A frameset document</TITLE>
</HEAD>
<FRAMESET cols="33%,33%,33%">
<FRAMESET rows="*,200">
<FRAME src="contents_of_frame1.html" scrolling="no">
<FRAME src="contents_of_frame2.gif"
marginwidth="10" marginheight="15"
noresize>
</FRAMESET>
<FRAME src="contents_of_frame3.html" frameborder="0">
<FRAME src="contents_of_frame4.html" frameborder="0">
</FRAMESET>
</HTML>
16.3 Specifying target frame information
Note. For information about current practice in determining the target
of a frame, please consult the notes on frames in the appendix.
Attribute definitions
target = frame-target [CI]
This attribute specifies the name of a frame where a document
is to be opened.
By assigning a name to a frame via the name attribute, authors can
refer to it as the "target" of links defined by other elements. The
target attribute may be set for elements that create links (A, LINK),
image maps (AREA), and forms (FORM).
Please consult the section on target frame names for information about
recognized frame names.
This example illustrates how targets allow the dynamic modification of
a frame's contents. First we define a frameset in the document
frameset.html, shown here:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A frameset document</TITLE>
</HEAD>
<FRAMESET rows="50%,50%">
<FRAME name="fixed" src="init_fixed.html">
<FRAME name="dynamic" src="init_dynamic.html">
</FRAMESET>
</HTML>
Then, in init_dynamic.html, we link to the frame named "dynamic".
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<HTML>
<HEAD>
<TITLE>A document with anchors with specific targets</TITLE>
</HEAD>
<BODY>
...beginning of the document...
<P>Now you may advance to
<A href="slide2.html" target="dynamic">slide 2.</A>
...more document...
<P>You're doing great. Now on to
<A href="slide3.html" target="dynamic">slide 3.</A>
</BODY>
</HTML>
Activating either link opens a new document in the frame named
"dynamic" while the other frame, "fixed", maintains its initial
contents.
Note. A frameset definition never changes, but the contents of one of
its frames can. Once the initial contents of a frame change, the
frameset definition no longer reflects the current state of its
frames.
There is currently no way to encode the entire state of a frameset in
a URI. Therefore, many user agents do not allow users to assign a
bookmark to a frameset.
Framesets may make navigation forward and backward through your user
agent's history more difficult for users.
16.3.1 Setting the default target for links
When many links in the same document designate the same target, it is
possible to specify the target once and dispense with the target
attribute of each element. This is done by setting the target
attribute of the BASE element.
We return to the previous example, this time factoring the target
information by defining it in the BASE element and removing it from
the A elements.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<HTML>
<HEAD>
<TITLE>A document with BASE with a specific target</TITLE>
<BASE href="http://www.mycom.com/Slides" target="dynamic">
</HEAD>
<BODY>
...beginning of the document...
<P>Now you may advance to <A href="slide2.html">slide 2.</A>
...more document...
<P>You're doing great. Now on to
<A href="slide3.html">slide 3.</A>
</BODY>
</HTML>
16.3.2 Target semantics
User agents should determine the target frame in which to load a
linked resource according to the following precedences (highest
priority to lowest):
1. If an element has its target attribute set to a known frame, when
the element is activated (i.e., a link is followed or a form is
processed), the resource designated by the element should be
loaded into the target frame.
2. If an element does not have the target attribute set but the BASE
element does, the BASE element's target attribute determines the
frame.
3. If neither the element nor the BASE element refers to a target,
the resource designated by the element should be loaded into the
frame containing the element.
4. If any target attribute refers to an unknown frame F, the user
agent should create a new window and frame, assign the name F to
the frame, and load the resource designated by the element in the
new frame.
User agents may provide users with a mechanism to override the target
attribute.
16.4 Alternate content
Authors should supply alternate content for those user agents that do
not support frames or are configured not to display frames.
16.4.1 The NOFRAMES element
<![ %HTML.Frameset; [
<!ENTITY % noframes.content "(BODY) -(NOFRAMES)">
]]>
<!ENTITY % noframes.content "(%flow;)*">
<!ELEMENT NOFRAMES - - %noframes.content;
-- alternate content container for non frame-based rendering -->
<!ATTLIST NOFRAMES
%attrs; -- %coreattrs, %i18n, %events --
>
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
The NOFRAMES element specifies content that should be displayed only
by user agents that do not support frames or are configured not to
display frames. User agents that support frames must only display the
contents of a NOFRAMES declaration when configured not to display
frames. User agents that do not support frames must display the
contents of NOFRAMES in any case.
The NOFRAMES element is part of both the transitional and frameset
DTDs. In a document that uses the frameset DTD, NOFRAMES may be used
at the end of the FRAMESET section of the document.
For example:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A frameset document with NOFRAMES</TITLE>
</HEAD>
<FRAMESET cols="50%, 50%">
<FRAME src="main.html">
<FRAME src="table_of_contents.html">
<NOFRAMES>
<P>Here is the <A href="main-noframes.html">
non-frame based version of the document.</A>
</NOFRAMES>
</FRAMESET>
</HTML>
NOFRAMES may be used, for example, in a document that is the source of
a frame and that uses the transitional DTD. This allows authors to
explain the document's purpose in cases when it is viewed out of the
frameset or with a user agent that doesn't support frames.
16.4.2 Long descriptions of frames
The longdesc attribute allows authors to make frame documents more
accessible to people using non-visual user agents. This attribute
designates a resource that provides a long description of the frame.
Authors should note that long descriptions associated with frames are
attached to the frame, not the frame's contents. Since the contents
may vary over time, the initial long description is likely to become
inappropriate for the frame's later contents. In particular, authors
should not include an image as the sole content of a frame.
The following frameset document describes two frames. The left frame
contains a table of contents and the right frame initially contains an
image of an ostrich:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A poorly-designed frameset document</TITLE>
</HEAD>
<FRAMESET cols="20%, 80%">
<FRAME src="table_of_contents.html">
<FRAME src="ostrich.gif" longdesc="ostrich-desc.html">
</FRAMESET>
</HTML>
Note that the image has been included in the frame independently of
any HTML element, so the author has no means of specifying alternate
text other than via the longdesc attribute. If the contents of the
right frame change (e.g., the user selects a rattlesnake from the
table of contents), users will have no textual access to the frame's
new content.
Thus, authors should not put an image directly in a frame. Instead,
the image should be specified in a separate HTML document, and therein
annotated with the appropriate alternate text:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A well-designed frameset document</TITLE>
</HEAD>
<FRAMESET cols="20%, 80%">
<FRAME src="table_of_contents.html">
<FRAME src="ostrich-container.html">
</FRAMESET>
</HTML>
<!-- In ostrich-container.html: -->
<HTML>
<HEAD>
<TITLE>The fast and powerful ostrich</TITLE>
</HEAD>
<P>
<OBJECT data="ostrich.gif" type="image/gif">
These ostriches sure taste good!
</OBJECT>
</HTML>
16.5 Inline frames: the IFRAME element
<!ELEMENT IFRAME - - (%flow;)* -- inline subwindow -->
<!ATTLIST IFRAME
%coreattrs; -- id, class, style, title --
longdesc %URI; #IMPLIED -- link to long description
(complements title) --
name CDATA #IMPLIED -- name of frame for targetting --
src %URI; #IMPLIED -- source of frame content --
frameborder (1|0) 1 -- request frame borders? --
marginwidth %Pixels; #IMPLIED -- margin widths in pixels --
marginheight %Pixels; #IMPLIED -- margin height in pixels --
scrolling (yes|no|auto) auto -- scrollbar or none --
align %IAlign; #IMPLIED -- vertical or horizontal alignment --
height %Length; #IMPLIED -- frame height --
width %Length; #IMPLIED -- frame width --
>
Attribute definitions
longdesc = uri [CT]
This attribute specifies a link to a long description of the
frame. This description should supplement the short description
provided using the title attribute, and is particularly useful
for non-visual user agents.
name = cdata [CI]
This attribute assigns a name to the current frame. This name
may be used as the target of subsequent links.
width = length [CN]
The width of the inline frame.
height = length [CN]
The height of the inline frame.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* title (element title)
* style (inline style information)
* name, src, frameborder, marginwidth, marginheight, scrolling
(frame controls and decoration)
* align (alignment)
The IFRAME element allows authors to insert a frame within a block of
text. Inserting an inline frame within a section of text is much like
inserting an object via the OBJECT element: they both allow you to
insert an HTML document in the middle of another, they may both be
aligned with surrounding text, etc.
The information to be inserted inline is designated by the src
attribute of this element. The contents of the IFRAME element, on the
other hand, should only be displayed by user agents that do not
support frames or are configured not to display frames.
For user agents that support frames, the following example will place
an inline frame surrounded by a border in the middle of the text.
<IFRAME src="foo.html" width="400" height="500"
scrolling="auto" frameborder="1">
[Your user agent does not support frames or is currently configured
not to display frames. However, you may visit
<A href="foo.html">the related document.</A>]
</IFRAME>
Inline frames may not be resized (and thus, they do not take the
noresize attribute).
Note. HTML documents may also be embedded in other HTML documents with
the OBJECT element. See the section on embedded documents for details.
17 Forms
Contents
1. Introduction to forms
2. Controls
1. Control types
3. The FORM element
4. The INPUT element
1. Control types created with INPUT
2. Examples of forms containing INPUT controls
5. The BUTTON element
6. The SELECT, OPTGROUP, and OPTION elements
1. Pre-selected options
7. The TEXTAREA element
8. The ISINDEX element
9. Labels
1. The LABEL element
10. Adding structure to forms: the FIELDSET and LEGEND elements
11. Giving focus to an element
1. Tabbing navigation
2. Access keys
12. Disabled and read-only controls
1. Disabled controls
2. Read-only controls
13. Form submission
1. Form submission method
2. Successful controls
3. Processing form data
o Step one: Identify the successful controls
o Step two: Build a form data set
o Step three: Encode the form data set
o Step four: Submit the encoded form data set
4. Form content types
o application/x-www-form-urlencoded
o multipart/form-data
17.1 Introduction to forms
An HTML form is a section of a document containing normal content,
markup, special elements called controls (checkboxes, radio buttons,
menus, etc.), and labels on those controls. Users generally "complete"
a form by modifying its controls (entering text, selecting menu items,
etc.), before submitting the form to an agent for processing (e.g., to
a Web server, to a mail server, etc.)
Here's a simple form that includes labels, radio buttons, and push
buttons (reset the form or submit it):
<FORM action="http://somesite.com/prog/adduser" method="post">
<P>
<LABEL for="firstname">First name: </LABEL>
<INPUT type="text" id="firstname"><BR>
<LABEL for="lastname">Last name: </LABEL>
<INPUT type="text" id="lastname"><BR>
<LABEL for="email">email: </LABEL>
<INPUT type="text" id="email"><BR>
<INPUT type="radio" name="sex" value="Male"> Male<BR>
<INPUT type="radio" name="sex" value="Female"> Female<BR>
<INPUT type="submit" value="Send"> <INPUT type="reset">
</P>
</FORM>
Note. This specification includes more detailed information about
forms in the subsections on form display issues.
17.2 Controls
Users interact with forms through named controls.
A control's "control name" is given by its name attribute. The scope
of the name attribute for a control within a FORM element is the FORM
element.
Each control has both an initial value and a current value, both of
which are character strings. Please consult the definition of each
control for information about initial values and possible constraints
on values imposed by the control. In general, a control's "initial
value" may be specified with the control element's value attribute.
However, the initial value of a TEXTAREA element is given by its
contents, and the initial value of an OBJECT element in a form is
determined by the object implementation (i.e., it lies outside the
scope of this specification).
The control's "current value" is first set to the initial value.
Thereafter, the control's current value may be modified through user
interaction and scripts.
A control's initial value does not change. Thus, when a form is reset,
each control's current value is reset to its initial value. If a
control does not have an initial value, the effect of a form reset on
that control is undefined.
When a form is submitted for processing, some controls have their name
paired with their current value and these pairs are submitted with the
form. Those controls for which name/value pairs are submitted are
called successful controls.
17.2.1 Control types
HTML defines the following control types:
buttons
Authors may create three types of buttons:
+ submit buttons: When activated, a submit button submits a
form. A form may contain more than one submit button.
+ reset buttons: When activated, a reset button resets all
controls to their initial values.
+ push buttons: Push buttons have no default behavior. Each
push button may have client-side scripts associated with the
element's event attributes. When an event occurs (e.g., the
user presses the button, releases it, etc.), the associated
script is triggered.
Authors should specify the scripting language of a push
button script through a default script declaration (with the
META element).
Authors create buttons with the BUTTON element or the INPUT
element. Please consult the definitions of these elements for
details about specifying different button types.
Note. Authors should note that the BUTTON element offers richer
rendering capabilities than the INPUT element.
checkboxes
Checkboxes (and radio buttons) are on/off switches that may be
toggled by the user. A switch is "on" when the control
element's checked attribute is set. When a form is submitted,
only "on" checkbox controls can become successful.
Several checkboxes in a form may share the same control name.
Thus, for example, checkboxes allow users to select several
values for the same property. The INPUT element is used to
create a checkbox control.
radio buttons
Radio buttons are like checkboxes except that when several
share the same control name, they are mutually exclusive: when
one is switched "on", all others with the same name are
switched "off". The INPUT element is used to create a radio
button control.
If no radio button in a set sharing the same control name is
initially "on", user agent behavior for choosing which control
is initially "on" is undefined. Note. Since existing
implementations handle this case differently, the current
specification differs from RFC 1866 ([RFC1866] section
8.1.2.4), which states:
At all times, exactly one of the radio buttons in a set is checked.
If none of the <INPUT> elements of a set of radio buttons specifies
`CHECKED', then the user agent must check the first radio button of
the set initially.
Since user agent behavior differs, authors should ensure that
in each set of radio buttons that one is initially "on".
menus
Menus offer users options from which to choose. The SELECT
element creates a menu, in combination with the OPTGROUP and
OPTION elements.
text input
Authors may create two types of controls that allow users to
input text. The INPUT element creates a single-line input
control and the TEXTAREA element creates a multi-line input
control. In both cases, the input text becomes the control's
current value.
file select
This control type allows the user to select files so that their
contents may be submitted with a form. The INPUT element is
used to create a file select control.
hidden controls
Authors may create controls that are not rendered but whose
values are submitted with a form. Authors generally use this
control type to store information between client/server
exchanges that would otherwise be lost due to the stateless
nature of HTTP (see [RFC2616]). The INPUT element is used to
create a hidden control.
object controls
Authors may insert generic objects in forms such that
associated values are submitted along with other controls.
Authors create object controls with the OBJECT element.
The elements used to create controls generally appear inside a FORM
element, but may also appear outside of a FORM element declaration
when they are used to build user interfaces. This is discussed in the
section on intrinsic events. Note that controls outside a form cannot
be successful controls.
17.3 The FORM element
<!ELEMENT FORM - - (%block;|SCRIPT)+ -(FORM) -- interactive form -->
<!ATTLIST FORM
%attrs; -- %coreattrs, %i18n, %events --
action %URI; #REQUIRED -- server-side form handler --
method (GET|POST) GET -- HTTP method used to submit the form--
enctype %ContentType; "application/x-www-form-urlencoded"
accept %ContentTypes; #IMPLIED -- list of MIME types for file upload --
name CDATA #IMPLIED -- name of form for scripting --
onsubmit %Script; #IMPLIED -- the form was submitted --
onreset %Script; #IMPLIED -- the form was reset --
accept-charset %Charsets; #IMPLIED -- list of supported charsets --
>
Start tag: required, End tag: required
Attribute definitions
action = uri [CT]
This attribute specifies a form processing agent. User agent
behavior for a value other than an HTTP URI is undefined.
method = get|post [CI]
This attribute specifies which HTTP method will be used to
submit the form data set. Possible (case-insensitive) values
are "get" (the default) and "post". See the section on form
submission for usage information.
enctype = content-type [CI]
This attribute specifies the content type used to submit the
form to the server (when the value of method is "post"). The
default value for this attribute is
"application/x-www-form-urlencoded". The value
"multipart/form-data" should be used in combination with the
INPUT element, type="file".
accept-charset = charset list [CI]
This attribute specifies the list of character encodings for
input data that is accepted by the server processing this form.
The value is a space- and/or comma-delimited list of charset
values. The client must interpret this list as an exclusive-or
list, i.e., the server is able to accept any single character
encoding per entity received.
The default value for this attribute is the reserved string
"UNKNOWN". User agents may interpret this value as the
character encoding that was used to transmit the document
containing this FORM element.
accept = content-type-list [CI]
This attribute specifies a comma-separated list of content
types that a server processing this form will handle correctly.
User agents may use this information to filter out
non-conforming files when prompting a user to select files to
be sent to the server (cf. the INPUT element when type="file").
name = cdata [CI]
This attribute names the element so that it may be referred to
from style sheets or scripts. Note. This attribute has been
included for backwards compatibility. Applications should use
the id attribute to identify elements.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* style (inline style information)
* title (element title)
* target (target frame information)
* onsubmit, onreset, onclick, ondblclick, onmousedown, onmouseup,
onmouseover, onmousemove, onmouseout, onkeypress, onkeydown,
onkeyup (intrinsic events)
The FORM element acts as a container for controls. It specifies:
* The layout of the form (given by the contents of the element).
* The program that will handle the completed and submitted form (the
action attribute). The receiving program must be able to parse
name/value pairs in order to make use of them.
* The method by which user data will be sent to the server (the
method attribute).
* A character encoding that must be accepted by the server in order
to handle this form (the accept-charset attribute). User agents
may advise the user of the value of the accept-charset attribute
and/or restrict the user's ability to enter unrecognized
characters.
A form can contain text and markup (paragraphs, lists, etc.) in
addition to form controls.
The following example shows a form that is to be processed by the
"adduser" program when submitted. The form will be sent to the program
using the HTTP "post" method.
<FORM action="http://somesite.com/prog/adduser" method="post">
...form contents...
</FORM>
Please consult the section on form submission for information about
how user agents must prepare form data for servers and how user agents
should handle expected responses.
Note. Further discussion on the behavior of servers that receive form
data is beyond the scope of this specification.
17.4 The INPUT element
<!ENTITY % InputType
"(TEXT | PASSWORD | CHECKBOX |
RADIO | SUBMIT | RESET |
FILE | HIDDEN | IMAGE | BUTTON)"
>
<!-- attribute name required for all but submit and reset -->
<!ELEMENT INPUT - O EMPTY -- form control -->
<!ATTLIST INPUT
%attrs; -- %coreattrs, %i18n, %events --
type %InputType; TEXT -- what kind of widget is needed --
name CDATA #IMPLIED -- submit as part of form --
value CDATA #IMPLIED -- Specify for radio buttons and checkbo
xes --
checked (checked) #IMPLIED -- for radio buttons and check boxes --
disabled (disabled) #IMPLIED -- unavailable in this context --
readonly (readonly) #IMPLIED -- for text and passwd --
size CDATA #IMPLIED -- specific to each type of field --
maxlength NUMBER #IMPLIED -- max chars for text fields --
src %URI; #IMPLIED -- for fields with images --
alt CDATA #IMPLIED -- short description --
usemap %URI; #IMPLIED -- use client-side image map --
ismap (ismap) #IMPLIED -- use server-side image map --
tabindex NUMBER #IMPLIED -- position in tabbing order --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
onselect %Script; #IMPLIED -- some text was selected --
onchange %Script; #IMPLIED -- the element value was changed --
accept %ContentTypes; #IMPLIED -- list of MIME types for file upload --
>
Start tag: required, End tag: forbidden
Attribute definitions
type =
text|password|checkbox|radio|submit|reset|file|hidden|image|butt
on [CI]
This attribute specifies the type of control to create. The
default value for this attribute is "text".
name = cdata [CI]
This attribute assigns the control name.
value = cdata [CA]
This attribute specifies the initial value of the control. It
is optional except when the type attribute has the value
"radio" or "checkbox".
size = cdata [CN]
This attribute tells the user agent the initial width of the
control. The width is given in pixels except when type
attribute has the value "text" or "password". In that case, its
value refers to the (integer) number of characters.
maxlength = number [CN]
When the type attribute has the value "text" or "password",
this attribute specifies the maximum number of characters the
user may enter. This number may exceed the specified size, in
which case the user agent should offer a scrolling mechanism.
The default value for this attribute is an unlimited number.
checked [CI]
When the type attribute has the value "radio" or "checkbox",
this boolean attribute specifies that the button is on. User
agents must ignore this attribute for other control types.
src = uri [CT]
When the type attribute has the value "image", this attribute
specifies the location of the image to be used to decorate the
graphical submit button.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* alt (alternate text)
* align (alignment)
* accept (legal content types for a server)
* readonly (read-only input controls)
* disabled (disabled input controls)
* tabindex (tabbing navigation)
* accesskey (access keys)
* usemap (client-side image maps)
* ismap (server-side image maps)
* onfocus, onblur, onselect, onchange, onclick, ondblclick,
onmousedown, onmouseup, onmouseover, onmousemove, onmouseout,
onkeypress, onkeydown, onkeyup (intrinsic events)
17.4.1 Control types created with INPUT
The control type defined by the INPUT element depends on the value of
the type attribute:
text
Creates a single-line text input control.
password
Like "text", but the input text is rendered in such a way as to
hide the characters (e.g., a series of asterisks). This control
type is often used for sensitive input such as passwords. Note
that the current value is the text entered by the user, not the
text rendered by the user agent.
Note. Application designers should note that this mechanism affords
only light security protection. Although the password is masked by
user agents from casual observers, it is transmitted to the server in
clear text, and may be read by anyone with low-level access to the
network.
checkbox
Creates a checkbox.
radio
Creates a radio button.
submit
Creates a submit button.
image
Creates a graphical submit button. The value of the src
attribute specifies the URI of the image that will decorate the
button. For accessibility reasons, authors should provide
alternate text for the image via the alt attribute.
When a pointing device is used to click on the image, the form
is submitted and the click coordinates passed to the server.
The x value is measured in pixels from the left of the image,
and the y value in pixels from the top of the image. The
submitted data includes name.x=x-value and name.y=y-value where
"name" is the value of the name attribute, and x-value and
y-value are the x and y coordinate values, respectively.
If the server takes different actions depending on the location
clicked, users of non-graphical browsers will be disadvantaged.
For this reason, authors should consider alternate approaches:
+ Use multiple submit buttons (each with its own image) in
place of a single graphical submit button. Authors may use
style sheets to control the positioning of these buttons.
+ Use a client-side image map together with scripting.
reset
Creates a reset button.
button
Creates a push button. User agents should use the value of the
value attribute as the button's label.
hidden
Creates a hidden control.
file
Creates a file select control. User agents may use the value of
the value attribute as the initial file name.
17.4.2 Examples of forms containing INPUT controls
The following sample HTML fragment defines a simple form that allows
the user to enter a first name, last name, email address, and gender.
When the submit button is activated, the form will be sent to the
program specified by the action attribute.
<FORM action="http://somesite.com/prog/adduser" method="post">
<P>
First name: <INPUT type="text" name="firstname"><BR>
Last name: <INPUT type="text" name="lastname"><BR>
email: <INPUT type="text" name="email"><BR>
<INPUT type="radio" name="sex" value="Male"> Male<BR>
<INPUT type="radio" name="sex" value="Female"> Female<BR>
<INPUT type="submit" value="Send"> <INPUT type="reset">
</P>
</FORM>
This form might be rendered as follows:
An example form rendering.
In the section on the LABEL element, we discuss marking up labels such
as "First name".
In this next example, the JavaScript function name verify is triggered
when the "onclick" event occurs:
<HEAD>
<META http-equiv="Content-Script-Type" content="text/javascript">
</HEAD>
<BODY>
<FORM action="..." method="post">
<P>
<INPUT type="button" value="Click Me" onclick="verify()">
</FORM>
</BODY>
Please consult the section on intrinsic events for more information
about scripting and events.
The following example shows how the contents of a user-specified file
may be submitted with a form. The user is prompted for his or her name
and a list of file names whose contents should be submitted with the
form. By specifying the enctype value of "multipart/form-data", each
file's contents will be packaged for submission in a separate section
of a multipart document.
<FORM action="http://server.dom/cgi/handle"
enctype="multipart/form-data"
method="post">
<P>
What is your name? <INPUT type="text" name="name_of_sender">
What files are you sending? <INPUT type="file" name="name_of_files">
</P>
</FORM>
17.5 The BUTTON element
<!ELEMENT BUTTON - -
(%flow;)* -(A|%formctrl;|FORM|FIELDSET)
-- push button -->
<!ATTLIST BUTTON
%attrs; -- %coreattrs, %i18n, %events --
name CDATA #IMPLIED
value CDATA #IMPLIED -- sent to server when submitted --
type (button|submit|reset) submit -- for use as form button --
disabled (disabled) #IMPLIED -- unavailable in this context --
tabindex NUMBER #IMPLIED -- position in tabbing order --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
>
Start tag: required, End tag: required
Attribute definitions
name = cdata [CI]
This attribute assigns the control name.
value = cdata [CS]
This attribute assigns the initial value to the button.
type = submit|button|reset [CI]
This attribute declares the type of the button. Possible
values:
+ submit: Creates a submit button. This is the default value.
+ reset: Creates a reset button.
+ button: Creates a push button.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* disabled (disabled input controls)
* accesskey (access keys)
* tabindex (tabbing navigation)
* onfocus, onblur, onclick, ondblclick, onmousedown, onmouseup,
onmouseover, onmousemove, onmouseout, onkeypress, onkeydown,
onkeyup (intrinsic events)
Buttons created with the BUTTON element function just like buttons
created with the INPUT element, but they offer richer rendering
possibilities: the BUTTON element may have content. For example, a
BUTTON element that contains an image functions like and may resemble
an INPUT element whose type is set to "image", but the BUTTON element
type allows content.
Visual user agents may render BUTTON buttons with relief and an
up/down motion when clicked, while they may render INPUT buttons as
"flat" images.
The following example expands a previous example, but creates submit
and reset buttons with BUTTON instead of INPUT. The buttons contain
images by way of the IMG element.
<FORM action="http://somesite.com/prog/adduser" method="post">
<P>
First name: <INPUT type="text" name="firstname"><BR>
Last name: <INPUT type="text" name="lastname"><BR>
email: <INPUT type="text" name="email"><BR>
<INPUT type="radio" name="sex" value="Male"> Male<BR>
<INPUT type="radio" name="sex" value="Female"> Female<BR>
<BUTTON name="submit" value="submit" type="submit">
Send<IMG src="/icons/wow.gif" alt="wow"></BUTTON>
<BUTTON name="reset" type="reset">
Reset<IMG src="/icons/oops.gif" alt="oops"></BUTTON>
</P>
</FORM>
Recall that authors must provide alternate text for an IMG element.
It is illegal to associate an image map with an IMG that appears as
the contents of a BUTTON element.
ILLEGAL EXAMPLE:
The following is not legal HTML.
<BUTTON>
<IMG src="foo.gif" usemap="...">
</BUTTON>
17.6 The SELECT, OPTGROUP, and OPTION elements
<!ELEMENT SELECT - - (OPTGROUP|OPTION)+ -- option selector -->
<!ATTLIST SELECT
%attrs; -- %coreattrs, %i18n, %events --
name CDATA #IMPLIED -- field name --
size NUMBER #IMPLIED -- rows visible --
multiple (multiple) #IMPLIED -- default is single selection --
disabled (disabled) #IMPLIED -- unavailable in this context --
tabindex NUMBER #IMPLIED -- position in tabbing order --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
onchange %Script; #IMPLIED -- the element value was changed --
>
Start tag: required, End tag: required
SELECT Attribute definitions
name = cdata [CI]
This attribute assigns the control name.
size = number [CN]
If a SELECT element is presented as a scrolled list box, this
attribute specifies the number of rows in the list that should
be visible at the same time. Visual user agents are not
required to present a SELECT element as a list box; they may
use any other mechanism, such as a drop-down menu.
multiple [CI]
If set, this boolean attribute allows multiple selections. If
not set, the SELECT element only permits single selections.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* disabled (disabled input controls)
* tabindex (tabbing navigation)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
The SELECT element creates a menu. Each choice offered by the menu is
represented by an OPTION element. A SELECT element must contain at
least one OPTION element.
The OPTGROUP element allows authors to group choices logically. This
is particularly helpful when the user must choose from a long list of
options; groups of related choices are easier to grasp and remember
than a single long list of options. In HTML 4, all OPTGROUP elements
must be specified directly within a SELECT element (i.e., groups may
not be nested).
17.6.1 Pre-selected options
Zero or more choices may be pre-selected for the user. User agents
should determine which choices are pre-selected as follows:
* If no OPTION element has the selected attribute set, user agent
behavior for choosing which option is initially selected is
undefined. Note. Since existing implementations handle this case
differently, the current specification differs from RFC 1866
([RFC1866] section 8.1.3), which states:
The initial state has the first option selected, unless a SELECTED
attribute is present on any of the <OPTION> elements.
Since user agent behavior differs, authors should ensure that each
menu includes a default pre-selected OPTION.
* If one OPTION element has the selected attribute set, it should be
pre-selected.
* If the SELECT element has the multiple attribute set and more than
one OPTION element has the selected attribute set, they should all
be pre-selected.
* It is considered an error if more than one OPTION element has the
selected attribute set and the SELECT element does not have the
multiple attribute set. User agents may vary in how they handle
this error, but should not pre-select more than one choice.
<!ELEMENT OPTGROUP - - (OPTION)+ -- option group -->
<!ATTLIST OPTGROUP
%attrs; -- %coreattrs, %i18n, %events --
disabled (disabled) #IMPLIED -- unavailable in this context --
label %Text; #REQUIRED -- for use in hierarchical menus --
>
Start tag: required, End tag: required
OPTGROUP Attribute definitions
label = text [CS]
This attribute specifies the label for the option group.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* disabled (disabled input controls)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
Note. Implementors are advised that future versions of HTML may extend
the grouping mechanism to allow for nested groups (i.e., OPTGROUP
elements may nest). This will allow authors to represent a richer
hierarchy of choices.
<!ELEMENT OPTION - O (#PCDATA) -- selectable choice -->
<!ATTLIST OPTION
%attrs; -- %coreattrs, %i18n, %events --
selected (selected) #IMPLIED
disabled (disabled) #IMPLIED -- unavailable in this context --
label %Text; #IMPLIED -- for use in hierarchical menus --
value CDATA #IMPLIED -- defaults to element content --
>
Start tag: required, End tag: optional
OPTION Attribute definitions
selected [CI]
When set, this boolean attribute specifies that this option is
pre-selected.
value = cdata [CS]
This attribute specifies the initial value of the control. If
this attribute is not set, the initial value is set to the
contents of the OPTION element.
label = text [CS]
This attribute allows authors to specify a shorter label for an
option than the content of the OPTION element. When specified,
user agents should use the value of this attribute rather than
the content of the OPTION element as the option label.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* disabled (disabled input controls)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
When rendering a menu choice, user agents should use the value of the
label attribute of the OPTION element as the choice. If this
attribute is not specified, user agents should use the contents of the
OPTION element.
The label attribute of the OPTGROUP element specifies the label for a
group of choices.
In this example, we create a menu that allows the user to select which
of seven software components to install. The first and second
components are pre-selected but may be deselected by the user. The
remaining components are not pre-selected. The size attribute states
that the menu should only have 4 rows even though the user may select
from among 7 options. The other options should be made available
through a scrolling mechanism.
The SELECT is followed by submit and reset buttons.
<FORM action="http://somesite.com/prog/component-select" method="post">
<P>
<SELECT multiple size="4" name="component-select">
<OPTION selected value="Component_1_a">Component_1</OPTION>
<OPTION selected value="Component_1_b">Component_2</OPTION>
<OPTION>Component_3</OPTION>
<OPTION>Component_4</OPTION>
<OPTION>Component_5</OPTION>
<OPTION>Component_6</OPTION>
<OPTION>Component_7</OPTION>
</SELECT>
<INPUT type="submit" value="Send"><INPUT type="reset">
</P>
</FORM>
Only selected options will be successful (using the control name
"component-select"). When no options are selected, the control is not
successful and neither the name nor any values are submitted to the
server when the form is submitted. Note that where the value attribute
is set, it determines the control's initial value, otherwise it's the
element's contents.
In this example we use the OPTGROUP element to group choices. The
following markup:
<FORM action="http://somesite.com/prog/someprog" method="post">
<P>
<SELECT name="ComOS">
<OPTION selected label="none" value="none">None</OPTION>
<OPTGROUP label="PortMaster 3">
<OPTION label="3.7.1" value="pm3_3.7.1">PortMaster 3 with ComOS 3.7.1</O
PTION>
<OPTION label="3.7" value="pm3_3.7">PortMaster 3 with ComOS 3.7</OPTION>
<OPTION label="3.5" value="pm3_3.5">PortMaster 3 with ComOS 3.5</OPTION>
</OPTGROUP>
<OPTGROUP label="PortMaster 2">
<OPTION label="3.7" value="pm2_3.7">PortMaster 2 with ComOS 3.7</OPTION>
<OPTION label="3.5" value="pm2_3.5">PortMaster 2 with ComOS 3.5</OPTION>
</OPTGROUP>
<OPTGROUP label="IRX">
<OPTION label="3.7R" value="IRX_3.7R">IRX with ComOS 3.7R</OPTION>
<OPTION label="3.5R" value="IRX_3.5R">IRX with ComOS 3.5R</OPTION>
</OPTGROUP>
</SELECT>
</FORM>
represents the following grouping:
None
PortMaster 3
3.7.1
3.7
3.5
PortMaster 2
3.7
3.5
IRX
3.7R
3.5R
Visual user agents may allow users to select from option groups
through a hierarchical menu or some other mechanism that reflects the
structure of choices.
A graphical user agent might render this as:
A possible rendering of OPTGROUP
This image shows a SELECT element rendered as cascading menus. The top
label of the menu displays the currently selected value (PortMaster 3,
3.7.1). The user has unfurled two cascading menus, but has not yet
selected the new value (PortMaster 2, 3.7). Note that each cascading
menu displays the label of an OPTGROUP or OPTION element.
17.7 The TEXTAREA element
<!ELEMENT TEXTAREA - - (#PCDATA) -- multi-line text field -->
<!ATTLIST TEXTAREA
%attrs; -- %coreattrs, %i18n, %events --
name CDATA #IMPLIED
rows NUMBER #REQUIRED
cols NUMBER #REQUIRED
disabled (disabled) #IMPLIED -- unavailable in this context --
readonly (readonly) #IMPLIED
tabindex NUMBER #IMPLIED -- position in tabbing order --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
onselect %Script; #IMPLIED -- some text was selected --
onchange %Script; #IMPLIED -- the element value was changed --
>
Start tag: required, End tag: required
Attribute definitions
name = cdata [CI]
This attribute assigns the control name.
rows = number [CN]
This attribute specifies the number of visible text lines.
Users should be able to enter more lines than this, so user
agents should provide some means to scroll through the contents
of the control when the contents extend beyond the visible
area.
cols = number [CN]
This attribute specifies the visible width in average character
widths. Users should be able to enter longer lines than this,
so user agents should provide some means to scroll through the
contents of the control when the contents extend beyond the
visible area. User agents may wrap visible text lines to keep
long lines visible without the need for scrolling.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* readonly (read-only input controls)
* disabled (disabled input controls)
* tabindex (tabbing navigation)
* onfocus, onblur, onselect, onchange, onclick, ondblclick,
onmousedown, onmouseup, onmouseover, onmousemove, onmouseout,
onkeypress, onkeydown, onkeyup (intrinsic events)
The TEXTAREA element creates a multi-line text input control. User
agents should use the contents of this element as the initial value of
the control and should render this text initially.
This example creates a TEXTAREA control that is 20 rows by 80 columns
and contains two lines of text initially. The TEXTAREA is followed by
submit and reset buttons.
<FORM action="http://somesite.com/prog/text-read" method="post">
<P>
<TEXTAREA name="thetext" rows="20" cols="80">
First line of initial text.
Second line of initial text.
</TEXTAREA>
<INPUT type="submit" value="Send"><INPUT type="reset">
</P>
</FORM>
Setting the readonly attribute allows authors to display unmodifiable
text in a TEXTAREA. This differs from using standard marked-up text in
a document because the value of TEXTAREA is submitted with the form.
17.8 The ISINDEX element
ISINDEX is deprecated. This element creates a single-line text input
control. Authors should use the INPUT element to create text input
controls.
See the Transitional DTD for the formal definition.
Attribute definitions
prompt = text [CS]
Deprecated. This attribute specifies a prompt string for the
input field.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
The ISINDEX element creates a single-line text input control that
allows any number of characters. User agents may use the value of the
prompt attribute as a title for the prompt.
DEPRECATED EXAMPLE:
The following ISINDEX declaration:
<ISINDEX prompt="Enter your search phrase: ">
could be rewritten with INPUT as follows:
<FORM action="..." method="post">
<P>Enter your search phrase: <INPUT type="text"></P>
</FORM>
Semantics of ISINDEX. Currently, the semantics for ISINDEX are only
well-defined when the base URI for the enclosing document is an HTTP
URI. In practice, the input string is restricted to Latin-1 as there
is no mechanism for the URI to specify a different character set.
17.9 Labels
Some form controls automatically have labels associated with them
(press buttons) while most do not (text fields, checkboxes and radio
buttons, and menus).
For those controls that have implicit labels, user agents should use
the value of the value attribute as the label string.
The LABEL element is used to specify labels for controls that do not
have implicit labels,
17.9.1 The LABEL element
<!ELEMENT LABEL - - (%inline;)* -(LABEL) -- form field label text -->
<!ATTLIST LABEL
%attrs; -- %coreattrs, %i18n, %events --
for IDREF #IMPLIED -- matches field ID value --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
>
Start tag: required, End tag: required
Attribute definitions
for = idref [CS]
This attribute explicitly associates the label being defined
with another control. When present, the value of this attribute
must be the same as the value of the id attribute of some other
control in the same document. When absent, the label being
defined is associated with the element's contents.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* accesskey (access keys)
* onfocus, onblur, onclick, ondblclick, onmousedown, onmouseup,
onmouseover, onmousemove, onmouseout, onkeypress, onkeydown,
onkeyup (intrinsic events)
The LABEL element may be used to attach information to controls. Each
LABEL element is associated with exactly one form control.
The for attribute associates a label with another control explicitly:
the value of the for attribute must be the same as the value of the id
attribute of the associated control element. More than one LABEL may
be associated with the same control by creating multiple references
via the for attribute.
This example creates a table that is used to align two text input
controls and their associated labels. Each label is associated
explicitly with one text input:
<FORM action="..." method="post">
<TABLE>
<TR>
<TD><LABEL for="fname">First Name</LABEL>
<TD><INPUT type="text" name="firstname" id="fname">
<TR>
<TD><LABEL for="lname">Last Name</LABEL>
<TD><INPUT type="text" name="lastname" id="lname">
</TABLE>
</FORM>
This example extends a previous example form to include LABEL
elements.
<FORM action="http://somesite.com/prog/adduser" method="post">
<P>
<LABEL for="firstname">First name: </LABEL>
<INPUT type="text" id="firstname"><BR>
<LABEL for="lastname">Last name: </LABEL>
<INPUT type="text" id="lastname"><BR>
<LABEL for="email">email: </LABEL>
<INPUT type="text" id="email"><BR>
<INPUT type="radio" name="sex" value="Male"> Male<BR>
<INPUT type="radio" name="sex" value="Female"> Female<BR>
<INPUT type="submit" value="Send"> <INPUT type="reset">
</P>
</FORM>
To associate a label with another control implicitly, the control
element must be within the contents of the LABEL element. In this
case, the LABEL may only contain one control element. The label itself
may be positioned before or after the associated control.
In this example, we implicitly associate two labels with two text
input controls:
<FORM action="..." method="post">
<P>
<LABEL>
First Name
<INPUT type="text" name="firstname">
</LABEL>
<LABEL>
<INPUT type="text" name="lastname">
Last Name
</LABEL>
</P>
</FORM>
Note that this technique cannot be used when a table is being used for
layout, with the label in one cell and its associated control in
another cell.
When a LABEL element receives focus, it passes the focus on to its
associated control. See the section below on access keys for examples.
Labels may be rendered by user agents in a number of ways (e.g.,
visually, read by speech synthesizers, etc.)
17.10 Adding structure to forms: the FIELDSET and LEGEND elements
<!--
#PCDATA is to solve the mixed content problem,
per specification only whitespace is allowed there!
-->
<!ELEMENT FIELDSET - - (#PCDATA,LEGEND,(%flow;)*) -- form control group -->
<!ATTLIST FIELDSET
%attrs; -- %coreattrs, %i18n, %events --
>
<!ELEMENT LEGEND - - (%inline;)* -- fieldset legend -->
<!ATTLIST LEGEND
%attrs; -- %coreattrs, %i18n, %events --
accesskey %Character; #IMPLIED -- accessibility key character --
>
Start tag: required, End tag: required
LEGEND Attribute definitions
align = top|bottom|left|right [CI]
Deprecated. This attribute specifies the position of the legend
with respect to the fieldset. Possible values:
+ top: The legend is at the top of the fieldset. This is the
default value.
+ bottom: The legend is at the bottom of the fieldset.
+ left: The legend is at the left side of the fieldset.
+ right: The legend is at the right side of the fieldset.
Attributes defined elsewhere
* id, class (document-wide identifiers)
* lang (language information), dir (text direction)
* title (element title)
* style (inline style information)
* accesskey (access keys)
* onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
(intrinsic events)
The FIELDSET element allows authors to group thematically related
controls and labels. Grouping controls makes it easier for users to
understand their purpose while simultaneously facilitating tabbing
navigation for visual user agents and speech navigation for
speech-oriented user agents. The proper use of this element makes
documents more accessible.
The LEGEND element allows authors to assign a caption to a FIELDSET.
The legend improves accessibility when the FIELDSET is rendered
non-visually.
In this example, we create a form that one might fill out at the
doctor's office. It is divided into three sections: personal
information, medical history, and current medication. Each section
contains controls for inputting the appropriate information.
<FORM action="..." method="post">
<P>
<FIELDSET>
<LEGEND>Personal Information</LEGEND>
Last Name: <INPUT name="personal_lastname" type="text" tabindex="1">
First Name: <INPUT name="personal_firstname" type="text" tabindex="2">
Address: <INPUT name="personal_address" type="text" tabindex="3">
...more personal information...
</FIELDSET>
<FIELDSET>
<LEGEND>Medical History</LEGEND>
<INPUT name="history_illness"
type="checkbox"
value="Smallpox" tabindex="20"> Smallpox
<INPUT name="history_illness"
type="checkbox"
value="Mumps" tabindex="21"> Mumps
<INPUT name="history_illness"
type="checkbox"
value="Dizziness" tabindex="22"> Dizziness
<INPUT name="history_illness"
type="checkbox"
value="Sneezing" tabindex="23"> Sneezing
...more medical history...
</FIELDSET>
<FIELDSET>
<LEGEND>Current Medication</LEGEND>
Are you currently taking any medication?
<INPUT name="medication_now"
type="radio"
value="Yes" tabindex="35">Yes
<INPUT name="medication_now"
type="radio"
value="No" tabindex="35">No
If you are currently taking medication, please indicate
it in the space below:
<TEXTAREA name="current_medication"
rows="20" cols="50"
tabindex="40">
</TEXTAREA>
</FIELDSET>
</FORM>
Note that in this example, we might improve the visual presentation of
the form by aligning elements within each FIELDSET (with style
sheets), adding color and font information (with style sheets), adding
scripting (say, to only open the "current medication" text area if the
user indicates he or she is currently on medication), etc.
17.11 Giving focus to an element
In an HTML document, an element must receive focus from the user in
order to become active and perform its tasks. For example, users must
activate a link specified by the A element in order to follow the
specified link. Similarly, users must give a TEXTAREA focus in order
to enter text into it.
There are several ways to give focus to an element:
* Designate the element with a pointing device.
* Navigate from one element to the next with the keyboard. The
document's author may define a tabbing order that specifies the
order in which elements will receive focus if the user navigates
the document with the keyboard (see tabbing navigation). Once
selected, an element may be activated by some other key sequence.
* Select an element through an access key (sometimes called
"keyboard shortcut" or "keyboard accelerator").
17.11.1 Tabbing navigation
Attribute definitions
tabindex = number [CN]
This attribute specifies the position of the current element in
the tabbing order for the current document. This value must be
a number between 0 and 32767. User agents should ignore leading
zeros.
The tabbing order defines the order in which elements will receive
focus when navigated by the user via the keyboard. The tabbing order
may include elements nested within other elements.
Elements that may receive focus should be navigated by user agents
according to the following rules:
1. Those elements that support the tabindex attribute and assign a
positive value to it are navigated first. Navigation proceeds from
the element with the lowest tabindex value to the element with the
highest value. Values need not be sequential nor must they begin
with any particular value. Elements that have identical tabindex
values should be navigated in the order they appear in the
character stream.
2. Those elements that do not support the tabindex attribute or
support it and assign it a value of "0" are navigated next. These
elements are navigated in the order they appear in the character
stream.
3. Elements that are disabled do not participate in the tabbing
order.
The following elements support the tabindex attribute: A, AREA,
BUTTON, INPUT, OBJECT, SELECT, and TEXTAREA.
In this example, the tabbing order will be the BUTTON, the INPUT
elements in order (note that "field1" and the button share the same
tabindex, but "field1" appears later in the character stream), and
finally the link created by the A element.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>A document with FORM</TITLE>
</HEAD>
<BODY>
...some text...
<P>Go to the
<A tabindex="10" href="http://www.w3.org/">W3C Web site.</A>
...some more...
<BUTTON type="button" name="get-database"
tabindex="1" onclick="get-database">
Get the current database.
</BUTTON>
...some more...
<FORM action="..." method="post">
<P>
<INPUT tabindex="1" type="text" name="field1">
<INPUT tabindex="2" type="text" name="field2">
<INPUT tabindex="3" type="submit" name="submit">
</P>
</FORM>
</BODY>
</HTML>
Tabbing keys. The actual key sequence that causes tabbing navigation
or element activation depends on the configuration of the user agent
(e.g., the "tab" key is used for navigation and the "enter" key is
used to activate a selected element).
User agents may also define key sequences to navigate the tabbing
order in reverse. When the end (or beginning) of the tabbing order is
reached, user agents may circle back to the beginning (or end).
17.11.2 Access keys
Attribute definitions
accesskey = character [CN]
This attribute assigns an access key to an element. An access
key is a single character from the document character set.
Note. Authors should consider the input method of the expected
reader when specifying an accesskey.
Pressing an access key assigned to an element gives focus to the
element. The action that occurs when an element receives focus depends
on the element. For example, when a user activates a link defined by
the A element, the user agent generally follows the link. When a user
activates a radio button, the user agent changes the value of the
radio button. When the user activates a text field, it allows input,
etc.
The following elements support the accesskey attribute: A, AREA,
BUTTON, INPUT, LABEL, and LEGEND, and TEXTAREA.
This example assigns the access key "U" to a label associated with an
INPUT control. Typing the access key gives focus to the label which
in turn gives it to the associated control. The user may then enter
text into the INPUT area.
<FORM action="..." method="post">
<P>
<LABEL for="fuser" accesskey="U">
User Name
</LABEL>
<INPUT type="text" name="user" id="fuser">
</P>
</FORM>
In this example, we assign an access key to a link defined by the A
element. Typing this access key takes the user to another document, in
this case, a table of contents.
<P><A accesskey="C"
rel="contents"
href="http://someplace.com/specification/contents.html">
Table of Contents</A>
The invocation of access keys depends on the underlying system. For
instance, on machines running MS Windows, one generally has to press
the "alt" key in addition to the access key. On Apple systems, one
generally has to press the "cmd" key in addition to the access key.
The rendering of access keys depends on the user agent. We recommend
that authors include the access key in label text or wherever the
access key is to apply. User agents should render the value of an
access key in such a way as to emphasize its role and to distinguish
it from other characters (e.g., by underlining it).
17.12 Disabled and read-only controls
In contexts where user input is either undesirable or irrelevant, it
is important to be able to disable a control or render it read-only.
For example, one may want to disable a form's submit button until the
user has entered some required data. Similarly, an author may want to
include a piece of read-only text that must be submitted as a value
along with the form. The following sections describe disabled and
read-only controls.
17.12.1 Disabled controls
Attribute definitions
disabled [CI]
When set for a form control, this boolean attribute disables
the control for user input.
When set, the disabled attribute has the following effects on an
element:
* Disabled controls do not receive focus.
* Disabled controls are skipped in tabbing navigation.
* Disabled controls cannot be successful.
The following elements support the disabled attribute: BUTTON, INPUT,
OPTGROUP, OPTION, SELECT, and TEXTAREA.
This attribute is inherited but local declarations override the
inherited value.
How disabled elements are rendered depends on the user agent. For
example, some user agents "gray out" disabled menu items, button
labels, etc.
In this example, the INPUT element is disabled. Therefore, it cannot
receive user input nor will its value be submitted with the form.
<INPUT disabled name="fred" value="stone">
Note. The only way to modify dynamically the value of the disabled
attribute is through a script.
17.12.2 Read-only controls
Attribute definitions
readonly [CI]
When set for a form control, this boolean attribute prohibits
changes to the control.
The readonly attribute specifies whether the control may be modified
by the user.
When set, the readonly attribute has the following effects on an
element:
* Read-only elements receive focus but cannot be modified by the
user.
* Read-only elements are included in tabbing navigation.
* Read-only elements may be successful.
The following elements support the readonly attribute: INPUT and
TEXTAREA.
How read-only elements are rendered depends on the user agent.
Note. The only way to modify dynamically the value of the readonly
attribute is through a script.
17.13 Form submission
The following sections explain how user agents submit form data to
form processing agents.
17.13.1 Form submission method
The method attribute of the FORM element specifies the HTTP method
used to send the form to the processing agent. This attribute may take
two values:
* get: With the HTTP "get" method, the form data set is appended to
the URI specified by the action attribute (with a question-mark
("?") as separator) and this new URI is sent to the processing
agent.
* post: With the HTTP "post" method, the form data set is included
in the body of the form and sent to the processing agent.
The "get" method should be used when the form is idempotent (i.e.,
causes no side-effects). Many database searches have no visible
side-effects and make ideal applications for the "get" method.
If the service associated with the processing of a form causes side
effects (for example, if the form modifies a database or subscription
to a service), the "post" method should be used.
Note. The "get" method restricts form data set values to ASCII
characters. Only the "post" method (with
enctype="multipart/form-data") is specified to cover the entire
[ISO10646] character set.
17.13.2 Successful controls
A successful control is "valid" for submission. Every successful
control has its control name paired with its current value as part of
the submitted form data set. A successful control must be defined
within a FORM element and must have a control name.
However:
* Controls that are disabled cannot be successful.
* If a form contains more than one submit button, only the activated
submit button is successful.
* All "on" checkboxes may be successful.
* For radio buttons that share the same value of the name attribute,
only the "on" radio button may be successful.
* For menus, the control name is provided by a SELECT element and
values are provided by OPTION elements. Only selected options may
be successful. When no options are selected, the control is not
successful and neither the name nor any values are submitted to
the server when the form is submitted.
* The current value of a file select is a list of one or more file
names. Upon submission of the form, the contents of each file are
submitted with the rest of the form data. The file contents are
packaged according to the form's content type.
* The current value of an object control is determined by the
object's implementation.
If a control doesn't have a current value when the form is submitted,
user agents are not required to treat it as a successful control.
Furthermore, user agents should not consider the following controls
successful:
* Reset buttons.
* OBJECT elements whose declare attribute has been set.
Hidden controls and controls that are not rendered because of style
sheet settings may still be successful. For example:
<FORM action="..." method="post">
<P>
<INPUT type="password" style="display:none"
name="invisible-password"
value="mypassword">
</FORM>
will still cause a value to be paired with the name
"invisible-password" and submitted with the form.
17.13.3 Processing form data
When the user submits a form (e.g., by activating a submit button),
the user agent processes it as follows.
Step one: Identify the successful controls
Step two: Build a form data set
A form data set is a sequence of control-name/current-value pairs
constructed from successful controls
Step three: Encode the form data set
The form data set is then encoded according to the content type
specified by the enctype attribute of the FORM element.
Step four: Submit the encoded form data set
Finally, the encoded data is sent to the processing agent designated
by the action attribute using the protocol specified by the method
attribute.
This specification does not specify all valid submission methods or
content types that may be used with forms. However, HTML 4 user
agents must support the established conventions in the following
cases:
* If the method is "get" and the action is an HTTP URI, the user
agent takes the value of action, appends a `?' to it, then appends
the form data set, encoded using the
"application/x-www-form-urlencoded" content type. The user agent
then traverses the link to this URI. In this scenario, form data
are restricted to ASCII codes.
* If the method is "post" and the action is an HTTP URI, the user
agent conducts an HTTP "post" transaction using the value of the
action attribute and a message created according to the content
type specified by the enctype attribute.
For any other value of action or method, behavior is unspecified.
User agents should render the response from the HTTP "get" and "post"
transactions.
17.13.4 Form content types
The enctype attribute of the FORM element specifies the content type
used to encode the form data set for submission to the server. User
agents must support the content types listed below. Behavior for other
content types is unspecified.
Please also consult the section on escaping ampersands in URI
attribute values.
application/x-www-form-urlencoded
This is the default content type. Forms submitted with this content
type must be encoded as follows:
1. Control names and values are escaped. Space characters are
replaced by `+', and then reserved characters are escaped as
described in [RFC1738], section 2.2: Non-alphanumeric characters
are replaced by `%HH', a percent sign and two hexadecimal digits
representing the ASCII code of the character. Line breaks are
represented as "CR LF" pairs (i.e., `%0D%0A').
2. The control names/values are listed in the order they appear in
the document. The name is separated from the value by `=' and
name/value pairs are separated from each other by `&'.
multipart/form-data
Note. Please consult [RFC2388] for additional information about file
uploads, including backwards compatibility issues, the relationship
between "multipart/form-data" and other content types, performance
issues, etc.
Please consult the appendix for information about security issues for
forms.
The content type "application/x-www-form-urlencoded" is inefficient
for sending large quantities of binary data or text containing
non-ASCII characters. The content type "multipart/form-data" should be
used for submitting forms that contain files, non-ASCII data, and
binary data.
The content "multipart/form-data" follows the rules of all multipart
MIME data streams as outlined in [RFC2045]. The definition of
"multipart/form-data" is available at the [IANA] registry.
A "multipart/form-data" message contains a series of parts, each
representing a successful control. The parts are sent to the
processing agent in the same order the corresponding controls appear
in the document stream. Part boundaries should not occur in any of the
data; how this is done lies outside the scope of this specification.
As with all multipart MIME types, each part has an optional
"Content-Type" header that defaults to "text/plain". User agents
should supply the "Content-Type" header, accompanied by a "charset"
parameter.
Each part is expected to contain:
1. a "Content-Disposition" header whose value is "form-data".
2. a name attribute specifying the control name of the corresponding
control. Control names originally encoded in non-ASCII character
sets may be encoded using the method outlined in [RFC2045].
Thus, for example, for a control named "mycontrol", the corresponding
part would be specified:
Content-Disposition: form-data; name="mycontrol"
As with all MIME transmissions, "CR LF" (i.e., `%0D%0A') is used to
separate lines of data.
Each part may be encoded and the "Content-Transfer-Encoding" header
supplied if the value of that part does not conform to the default
(7BIT) encoding (see [RFC2045], section 6)
If the contents of a file are submitted with a form, the file input
should be identified by the appropriate content type (e.g.,
"application/octet-stream"). If multiple files are to be returned as
the result of a single form entry, they should be returned as
"multipart/mixed" embedded within the "multipart/form-data".
The user agent should attempt to supply a file name for each submitted
file. The file name may be specified with the "filename" parameter of
the 'Content-Disposition: form-data' header, or, in the case of
multiple files, in a 'Content-Disposition: file' header of the
subpart. If the file name of the client's operating system is not in
US-ASCII, the file name might be approximated or encoded using the
method of [RFC2045]. This is convenient for those cases where, for
example, the uploaded files might contain references to each other
(e.g., a TeX file and its ".sty" auxiliary style description).
The following example illustrates "multipart/form-data" encoding.
Suppose we have the following form:
<FORM action="http://server.com/cgi/handle"
enctype="multipart/form-data"
method="post">
<P>
What is your name? <INPUT type="text" name="submit-name"><BR>
What files are you sending? <INPUT type="file" name="files"><BR>
<INPUT type="submit" value="Send"> <INPUT type="reset">
</FORM>
If the user enters "Larry" in the text input, and selects the text
file "file1.txt", the user agent might send back the following data:
Content-Type: multipart/form-data; boundary=AaB03x
--AaB03x
Content-Disposition: form-data; name="submit-name"
Larry
--AaB03x
Content-Disposition: form-data; name="files"; filename="file1.txt"
Content-Type: text/plain
... contents of file1.txt ...
--AaB03x--
If the user selected a second (image) file "file2.gif", the user agent
might construct the parts as follows:
Content-Type: multipart/form-data; boundary=AaB03x
--AaB03x
Content-Disposition: form-data; name="submit-name"
Larry
--AaB03x
Content-Disposition: form-data; name="files"
Content-Type: multipart/mixed; boundary=BbC04y
--BbC04y
Content-Disposition: file; filename="file1.txt"
Content-Type: text/plain
... contents of file1.txt ...
--BbC04y
Content-Disposition: file; filename="file2.gif"
Content-Type: image/gif
Content-Transfer-Encoding: binary
...contents of file2.gif...
--BbC04y--
--AaB03x--
18 Scripts
Contents
1. Introduction to scripts
2. Designing documents for user agents that support scripting
1. The SCRIPT element
2. Specifying the scripting language
o The default scripting language
o Local declaration of a scripting language
o References to HTML elements from a script
3. Intrinsic events
4. Dynamic modification of documents
3. Designing documents for user agents that don't support scripting
1. The NOSCRIPT element
2. Hiding script data from user agents
18.1 Introduction to scripts
A client-side script is a program that may accompany an HTML document
or be embedded directly in it. The program executes on the client's
machine when the document loads, or at some other time such as when a
link is activated. HTML's support for scripts is independent of the
scripting language.
Scripts offer authors a means to extend HTML documents in highly
active and interactive ways. For example:
* Scripts may be evaluated as a document loads to modify the
contents of the document dynamically.
* Scripts may accompany a form to process input as it is entered.
Designers may dynamically fill out parts of a form based on the
values of other fields. They may also ensure that input data
conforms to predetermined ranges of values, that fields are
mutually consistent, etc.
* Scripts may be triggered by events that affect the document, such
as loading, unloading, element focus, mouse movement, etc.
* Scripts may be linked to form controls (e.g., buttons) to produce
graphical user interface elements.
There are two types of scripts authors may attach to an HTML document:
* Those that are executed one time when the document is loaded by
the user agent. Scripts that appear within a SCRIPT element are
executed when the document is loaded. For user agents that cannot
or will not handle scripts, authors may include alternate content
via the NOSCRIPT element.
* Those that are executed every time a specific event occurs. These
scripts may be assigned to a number of elements via the intrinsic
event attributes.
Note. This specification includes more detailed information about
scripting in sections on script macros.
18.2 Designing documents for user agents that support scripting
The following sections discuss issues that concern user agents that
support scripting.
18.2.1 The SCRIPT element
<!ELEMENT SCRIPT - - %Script; -- script statements -->
<!ATTLIST SCRIPT
charset %Charset; #IMPLIED -- char encoding of linked resource --
type %ContentType; #REQUIRED -- content type of script language --
src %URI; #IMPLIED -- URI for an external script --
defer (defer) #IMPLIED -- UA may defer execution of script --
>
Start tag: required, End tag: required
Attribute definitions
src = uri [CT]
This attribute specifies the location of an external script.
type = content-type [CI]
This attribute specifies the scripting language of the
element's contents and overrides the default scripting
language. The scripting language is specified as a content type
(e.g., "text/javascript"). Authors must supply a value for this
attribute. There is no default value for this attribute.
language = cdata [CI]
Deprecated. This attribute specifies the scripting language of
the contents of this element. Its value is an identifier for
the language, but since these identifiers are not standard,
this attribute has been deprecated in favor of type.
defer [CI]
When set, this boolean attribute provides a hint to the user
agent that the script is not going to generate any document
content (e.g., no "document.write" in javascript) and thus, the
user agent can continue parsing and rendering.
Attributes defined elsewhere
* charset(character encodings)
The SCRIPT element places a script within a document. This element may
appear any number of times in the HEAD or BODY of an HTML document.
The script may be defined within the contents of the SCRIPT element or
in an external file. If the src attribute is not set, user agents must
interpret the contents of the element as the script. If the src has a
URI value, user agents must ignore the element's contents and retrieve
the script via the URI. Note that the charset attribute refers to the
character encoding of the script designated by the src attribute; it
does not concern the content of the SCRIPT element.
Scripts are evaluated by script engines that must be known to a user
agent.
The syntax of script data depends on the scripting language.
18.2.2 Specifying the scripting language
As HTML does not rely on a specific scripting language, document
authors must explicitly tell user agents the language of each script.
This may be done either through a default declaration or a local
declaration.
The default scripting language
Authors should specify the default scripting language for all scripts
in a document by including the following META declaration in the HEAD:
<META http-equiv="Content-Script-Type" content="type">
where "type" is a content type naming the scripting language. Examples
of values include "text/tcl", "text/javascript", "text/vbscript".
In the absence of a META declaration, the default can be set by a
"Content-Script-Type" HTTP header.
Content-Script-Type: type
where "type" is again a content type naming the scripting language.
User agents should determine the default scripting language for a
document according to the following steps (highest to lowest
priority):
1. If any META declarations specify the "Content-Script-Type", the
last one in the character stream determines the default scripting
language.
2. Otherwise, if any HTTP headers specify the "Content-Script-Type",
the last one in the character stream determines the default
scripting language.
Documents that do not specify default scripting language information
and that contain elements that specify an intrinsic event script are
incorrect. User agents may still attempt to interpret incorrectly
specified scripts but are not required to. Authoring tools should
generate default scripting language information to help authors avoid
creating incorrect documents.
Local declaration of a scripting language
The type attribute must be specified for each SCRIPT element instance
in a document. The value of the type attribute for a SCRIPT element
overrides the default scripting language for that element.
In this example, we declare the default scripting language to be
"text/tcl". We include one SCRIPT in the header, whose script is
located in an external file and is in the scripting language
"text/vbscript". We also include one SCRIPT in the body, which
contains its own script written in "text/javascript".
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>A document with SCRIPT</TITLE>
<META http-equiv="Content-Script-Type" content="text/tcl">
<SCRIPT type="text/vbscript" src="http://someplace.com/progs/vbcalc">
</SCRIPT>
</HEAD>
<BODY>
<SCRIPT type="text/javascript">
...some JavaScript...
</SCRIPT>
</BODY>
</HTML>
References to HTML elements from a script
Each scripting language has its own conventions for referring to HTML
objects from within a script. This specification does not define a
standard mechanism for referring to HTML objects.
However, scripts should refer to an element according to its assigned
name. Scripting engines should observe the following precedence rules
when identifying an element: a name attribute takes precedence over an
id if both are set. Otherwise, one or the other may be used.
18.2.3 Intrinsic events
Note. Authors of HTML documents are advised that changes are likely to
occur in the realm of intrinsic events (e.g., how scripts are bound to
events). Research in this realm is carried on by members of the W3C
Document Object Model Working Group (see the W3C Web Site at
http://www.w3.org/ for more information).
Attribute definitions
onload = script [CT]
The onload event occurs when the user agent finishes loading a
window or all frames within a FRAMESET. This attribute may be
used with BODY and FRAMESET elements.
onunload = script [CT]
The onunload event occurs when the user agent removes a
document from a window or frame. This attribute may be used
with BODY and FRAMESET elements.
onclick = script [CT]
The onclick event occurs when the pointing device button is
clicked over an element. This attribute may be used with most
elements.
ondblclick = script [CT]
The ondblclick event occurs when the pointing device button is
double clicked over an element. This attribute may be used with
most elements.
onmousedown = script [CT]
The onmousedown event occurs when the pointing device button is
pressed over an element. This attribute may be used with most
elements.
onmouseup = script [CT]
The onmouseup event occurs when the pointing device button is
released over an element. This attribute may be used with most
elements.
onmouseover = script [CT]
The onmouseover event occurs when the pointing device is moved
onto an element. This attribute may be used with most elements.
onmousemove = script [CT]
The onmousemove event occurs when the pointing device is moved
while it is over an element. This attribute may be used with
most elements.
onmouseout = script [CT]
The onmouseout event occurs when the pointing device is moved
away from an element. This attribute may be used with most
elements.
onfocus = script [CT]
The onfocus event occurs when an element receives focus either
by the pointing device or by tabbing navigation. This attribute
may be used with the following elements: A, AREA, LABEL, INPUT,
SELECT, TEXTAREA, and BUTTON.
onblur = script [CT]
The onblur event occurs when an element loses focus either by
the pointing device or by tabbing navigation. It may be used
with the same elements as onfocus.
onkeypress = script [CT]
The onkeypress event occurs when a key is pressed and released
over an element. This attribute may be used with most elements.
onkeydown = script [CT]
The onkeydown event occurs when a key is pressed down over an
element. This attribute may be used with most elements.
onkeyup = script [CT]
The onkeyup event occurs when a key is released over an
element. This attribute may be used with most elements.
onsubmit = script [CT]
The onsubmit event occurs when a form is submitted. It only
applies to the FORM element.
onreset = script [CT]
The onreset event occurs when a form is reset. It only applies
to the FORM element.
onselect = script [CT]
The onselect event occurs when a user selects some text in a
text field. This attribute may be used with the INPUT and
TEXTAREA elements.
onchange = script [CT]
The onchange event occurs when a control loses the input focus
and its value has been modified since gaining focus. This
attribute applies to the following elements: INPUT, SELECT, and
TEXTAREA.
It is possible to associate an action with a certain number of events
that occur when a user interacts with a user agent. Each of the
"intrinsic events" listed above takes a value that is a script. The
script is executed whenever the event occurs for that element. The
syntax of script data depends on the scripting language.
Control elements such as INPUT, SELECT, BUTTON, TEXTAREA, and LABEL
all respond to certain intrinsic events. When these elements do not
appear within a form, they may be used to augment the graphical user
interface of the document.
For instance, authors may want to include press buttons in their
documents that do not submit a form but still communicate with a
server when they are activated.
The following examples show some possible control and user interface
behavior based on intrinsic events.
In the following example, userName is a required text field. When a
user attempts to leave the field, the onblur event calls a JavaScript
function to confirm that userName has an acceptable value.
<INPUT NAME="userName" onblur="validUserName(this.value)">
Here is another JavaScript example:
<INPUT NAME="num"
onchange="if (!checkNum(this.value, 1, 10))
{this.focus();this.select();} else {thanks()}"
VALUE="0">
Here is a VBScript example of an event handler for a text field:
<INPUT name="edit1" size="50">
<SCRIPT type="text/vbscript">
Sub edit1_changed()
If edit1.value = "abc" Then
button1.enabled = True
Else
button1.enabled = False
End If
End Sub
</SCRIPT>
Here is the same example using Tcl:
<INPUT name="edit1" size="50">
<SCRIPT type="text/tcl">
proc edit1_changed {} {
if {[edit value] == abc} {
button1 enable 1
} else {
button1 enable 0
}
}
edit1 onChange edit1_changed
</SCRIPT>
Here is a JavaScript example for event binding within a script. First,
here's a simple click handler:
<BUTTON type="button" name="mybutton" value="10">
<SCRIPT type="text/javascript">
function my_onclick() {
. . .
}
document.form.mybutton.onclick = my_onclick
</SCRIPT>
</BUTTON>
Here's a more interesting window handler:
<SCRIPT type="text/javascript">
function my_onload() {
. . .
}
var win = window.open("some/other/URI")
if (win) win.onload = my_onload
</SCRIPT>
In Tcl this looks like:
<SCRIPT type="text/tcl">
proc my_onload {} {
. . .
}
set win [window open "some/other/URI"]
if {$win != ""} {
$win onload my_onload
}
</SCRIPT>
Note that "document.write" or equivalent statements in intrinsic event
handlers create and write to a new document rather than modifying the
current one.
18.2.4 Dynamic modification of documents
Scripts that are executed when a document is loaded may be able to
modify the document's contents dynamically. The ability to do so
depends on the scripting language itself (e.g., the "document.write"
statement in the HTML object model supported by some vendors).
The dynamic modification of a document may be modeled as follows:
1. All SCRIPT elements are evaluated in order as the document is
loaded.
2. All script constructs within a given SCRIPT element that generate
SGML CDATA are evaluated. Their combined generated text is
inserted in the document in place of the SCRIPT element.
3. The generated CDATA is re-evaluated.
HTML documents are constrained to conform to the HTML DTD both before
and after processing any SCRIPT elements.
The following example illustrates how scripts may modify a document
dynamically. The following script:
<TITLE>Test Document</TITLE>
<SCRIPT type="text/javascript">
document.write("<p><b>Hello World!<\/b>")
</SCRIPT>
Has the same effect as this HTML markup:
<TITLE>Test Document</TITLE>
<P><B>Hello World!</B>
18.3 Designing documents for user agents that don't support scripting
The following sections discuss how authors may create documents that
work for user agents that don't support scripting.
18.3.1 The NOSCRIPT element
<!ELEMENT NOSCRIPT - - (%block;)+
-- alternate content container for non script-based rendering -->
<!ATTLIST NOSCRIPT
%attrs; -- %coreattrs, %i18n, %events --
>
Start tag: required, End tag: required
The NOSCRIPT element allows authors to provide alternate content when
a script is not executed. The content of a NOSCRIPT element should
only be rendered by a script-aware user agent in the following cases:
* The user agent is configured not to evaluate scripts.
* The user agent doesn't support a scripting language invoked by a
SCRIPT element earlier in the document.
User agents that do not support client-side scripts must render this
element's contents.
In the following example, a user agent that executes the SCRIPT will
include some dynamically created data in the document. If the user
agent doesn't support scripts, the user may still retrieve the data
through a link.
<SCRIPT type="text/tcl">
...some Tcl script to insert data...
</SCRIPT>
<NOSCRIPT>
<P>Access the <A href="http://someplace.com/data">data.</A>
</NOSCRIPT>
18.3.2 Hiding script data from user agents
User agents that don't recognize the SCRIPT element will likely render
that element's contents as text. Some scripting engines, including
those for languages JavaScript, VBScript, and Tcl allow the script
statements to be enclosed in an SGML comment. User agents that don't
recognize the SCRIPT element will thus ignore the comment while smart
scripting engines will understand that the script in comments should
be executed.
Another solution to the problem is to keep scripts in external
documents and refer to them with the src attribute.
Commenting scripts in JavaScript
The JavaScript engine allows the string "<!--" to occur at the start
of a SCRIPT element, and ignores further characters until the end of
the line. JavaScript interprets "//" as starting a comment extending
to the end of the current line. This is needed to hide the string
"-->" from the JavaScript parser.
<SCRIPT type="text/javascript">
<!-- to hide script contents from old browsers
function square(i) {
document.write("The call passed ", i ," to the function.","<BR>")
return i * i
}
document.write("The function returned ",square(5),".")
// end hiding contents from old browsers -->
</SCRIPT>
Commenting scripts in VBScript
In VBScript, a single quote character causes the rest of the current
line to be treated as a comment. It can therefore be used to hide the
string "-->" from VBScript, for instance:
<SCRIPT type="text/vbscript">
<!--
Sub foo()
...
End Sub
' -->
</SCRIPT>
Commenting scripts in TCL
In Tcl, the "#" character comments out the rest of the line:
<SCRIPT type="text/tcl">
<!-- to hide script contents from old browsers
proc square {i} {
document write "The call passed $i to the function.<BR>"
return [expr $i * $i]
}
document write "The function returned [square 5]."
# end hiding contents from old browsers -->
</SCRIPT>
Note. Some browsers close comments on the first ">" character, so to
hide script content from such browsers, you can transpose operands for
relational and shift operators (e.g., use "y < x" rather than "x > y")
or use scripting language-dependent escapes for ">".
19 SGML reference information for HTML
Contents
1. Document Validation
2. Sample SGML catalog
The following sections contain the formal SGML definition of HTML 4.
It includes the SGML declaration, the Document Type Definition (DTD),
and the Character entity references, as well as a sample SGML catalog.
These files are also available in ASCII format as listed below:
Default DTD:
strict.dtd
Transitional DTD:
loose.dtd
Frameset DTD:
frameset.dtd
SGML declaration:
HTML4.decl
Entity definition files:
HTMLspecial.ent
HTMLsymbol.ent
HTMLlat1.ent
A sample catalog:
HTML4.cat
19.1 Document Validation
Many authors rely on a limited set of browsers to check on the
documents they produce, assuming that if the browsers can render their
documents they are valid. Unfortunately, this is a very ineffective
means of verifying a document's validity precisely because browsers
are designed to cope with invalid documents by rendering them as well
as they can to avoid frustrating users.
For better validation, you should check your document against an SGML
parser such as nsgmls (see [SP]), to verify that HTML documents
conform to the HTML 4 DTD. If the document type declaration of your
document includes a URI and your SGML parser supports this type of
system identifier, it will get the DTD directly. Otherwise you can use
the following sample SGML catalog. It assumes that the DTD has been
saved as the file "strict.dtd" and that the entities are in the files
"HTMLlat1.ent", "HTMLsymbol.ent" and "HTMLspecial.ent". In any case,
make sure your SGML parser is capable of handling [ISO10646]. See your
validation tool documentation for further details.
Beware that such validation, although useful and highly recommended,
does not guarantee that a document fully conforms to the HTML 4
specification. This is because an SGML parser relies solely on the
given SGML DTD which does not express all aspects of a valid HTML 4
document. Specifically, an SGML parser ensures that the syntax, the
structure, the list of elements, and their attributes are valid. But
for instance, it cannot catch errors such as setting the width
attribute of an IMG element to an invalid value (i.e., "foo" or
"12.5"). Although the specification restricts the value for this
attribute to an "integer representing a length in pixels," the DTD
only defines it to be CDATA, which actually allows any value. Only a
specialized program could capture the complete specification of HTML
4.
Nevertheless, this type of validation is still highly recommended
since it permits the detection of a large set of errors that make
documents invalid.
19.2 Sample SGML catalog
This catalog includes the override directive to ensure that processing
software such as nsgmls uses public identifiers in preference to
system identifiers. This means that users do not have to be connected
to the Web when retrieving URI-based system identifiers.
OVERRIDE YES
PUBLIC "-//W3C//DTD HTML 4.01//EN" strict.dtd
PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" loose.dtd
PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN" frameset.dtd
PUBLIC "-//W3C//ENTITIES Latin1//EN//HTML" HTMLlat1.ent
PUBLIC "-//W3C//ENTITIES Special//EN//HTML" HTMLspecial.ent
PUBLIC "-//W3C//ENTITIES Symbols//EN//HTML" HTMLsymbol.ent
20 SGML Declaration of HTML 4
Note. The total number of codepoints allowed in the document character
set of this SGML declaration includes the first 17 planes of
[ISO10646] (17 times 65536). This limitation has been made because
this number is limited to a length of 8 digits in the current version
of the SGML standard. It does not imply any statement about the
feasibility of a long-term restriction of characters in UCS to the
first 17 planes. Chances are very high that the limitation to 8 digits
in SGML will be removed before, and that this specification will be
updated before, the first assignment of a character beyond the first
17 planes.
Note. Strictly speaking, ISO Registration Number 177 refers to the
original state of [ISO10646] in 1993. Changes since 1993 have been the
addition of characters and a one-time operation reallocating a large
number of codepoints for Korean Hangul (Amendment 5). Revisions of the
HTML 4 specification may update the reference to ISO 10646 to include
additional changes.
20.1 SGML Declaration
<!SGML "ISO 8879:1986 (WWW)"
--
SGML Declaration for HyperText Markup Language version HTML 4
With support for the first 17 planes of ISO 10646 and
increased limits for tag and literal lengths etc.
--
CHARSET
BASESET "ISO Registration Number 177//CHARSET
ISO/IEC 10646-1:1993 UCS-4 with
implementation level 3//ESC 2/5 2/15 4/6"
DESCSET 0 9 UNUSED
9 2 9
11 2 UNUSED
13 1 13
14 18 UNUSED
32 95 32
127 1 UNUSED
128 32 UNUSED
160 55136 160
55296 2048 UNUSED -- SURROGATES --
57344 1056768 57344
CAPACITY SGMLREF
TOTALCAP 150000
GRPCAP 150000
ENTCAP 150000
SCOPE DOCUMENT
SYNTAX
SHUNCHAR CONTROLS 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 127
BASESET "ISO 646IRV:1991//CHARSET
International Reference Version
(IRV)//ESC 2/8 4/2"
DESCSET 0 128 0
FUNCTION
RE 13
RS 10
SPACE 32
TAB SEPCHAR 9
NAMING LCNMSTRT ""
UCNMSTRT ""
LCNMCHAR ".-_:"
UCNMCHAR ".-_:"
NAMECASE GENERAL YES
ENTITY NO
DELIM GENERAL SGMLREF
HCRO "&#x" -- 38 is the number for ampersand --
SHORTREF SGMLREF
NAMES SGMLREF
QUANTITY SGMLREF
ATTCNT 60 -- increased --
ATTSPLEN 65536 -- These are the largest values --
LITLEN 65536 -- permitted in the declaration --
NAMELEN 65536 -- Avoid fixed limits in actual --
PILEN 65536 -- implementations of HTML UA's --
TAGLVL 100
TAGLEN 65536
GRPGTCNT 150
GRPCNT 64
FEATURES
MINIMIZE
DATATAG NO
OMITTAG YES
RANK NO
SHORTTAG YES
LINK
SIMPLE NO
IMPLICIT NO
EXPLICIT NO
OTHER
CONCUR NO
SUBDOC NO
FORMAL YES
APPINFO NONE
>
21 Document Type Definition
<!--
This is HTML 4.01 Strict DTD, which excludes the presentation
attributes and elements that W3C expects to phase out as
support for style sheets matures. Authors should use the Strict
DTD when possible, but may use the Transitional DTD when support
for presentation attribute and elements is required.
HTML 4 includes mechanisms for style sheets, scripting,
embedding objects, improved support for right to left and mixed
direction text, and enhancements to forms for improved
accessibility for people with disabilities.
Draft: $Date: 1999/12/24 23:37:46 $
Authors:
Dave Raggett <dsr@w3.org>
Arnaud Le Hors <lehors@w3.org>
Ian Jacobs <ij@w3.org>
Further information about HTML 4.01 is available at:
http://www.w3.org/TR/1999/REC-html401-19991224
The HTML 4.01 specification includes additional
syntactic constraints that cannot be expressed within
the DTDs.
-->
<!--
Typical usage:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
...
</head>
<body>
...
</body>
</html>
The URI used as a system identifier with the public identifier allows
the user agent to download the DTD and entity sets as needed.
The FPI for the Transitional HTML 4.01 DTD is:
"-//W3C//DTD HTML 4.01 Transitional//EN"
This version of the transitional DTD is:
http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd
If you are writing a document that includes frames, use
the following FPI:
"-//W3C//DTD HTML 4.01 Frameset//EN"
This version of the frameset DTD is:
http://www.w3.org/TR/1999/REC-html401-19991224/frameset.dtd
Use the following (relative) URIs to refer to
the DTDs and entity definitions of this specification:
"strict.dtd"
"loose.dtd"
"frameset.dtd"
"HTMLlat1.ent"
"HTMLsymbol.ent"
"HTMLspecial.ent"
-->
<!--================== Imported Names ====================================-->
<!-- Feature Switch for frameset documents -->
<!ENTITY % HTML.Frameset "IGNORE">
<!ENTITY % ContentType "CDATA"
-- media type, as per [RFC2045]
-->
<!ENTITY % ContentTypes "CDATA"
-- comma-separated list of media types, as per [RFC2045]
-->
<!ENTITY % Charset "CDATA"
-- a character encoding, as per [RFC2045]
-->
<!ENTITY % Charsets "CDATA"
-- a space-separated list of character encodings, as per [RFC2045]
-->
<!ENTITY % LanguageCode "NAME"
-- a language code, as per [RFC1766]
-->
<!ENTITY % Character "CDATA"
-- a single character from [ISO10646]
-->
<!ENTITY % LinkTypes "CDATA"
-- space-separated list of link types
-->
<!ENTITY % MediaDesc "CDATA"
-- single or comma-separated list of media descriptors
-->
<!ENTITY % URI "CDATA"
-- a Uniform Resource Identifier,
see [URI]
-->
<!ENTITY % Datetime "CDATA" -- date and time information. ISO date format -->
<!ENTITY % Script "CDATA" -- script expression -->
<!ENTITY % StyleSheet "CDATA" -- style sheet data -->
<!ENTITY % Text "CDATA">
<!-- Parameter Entities -->
<!ENTITY % head.misc "SCRIPT|STYLE|META|LINK|OBJECT" -- repeatable head element
s -->
<!ENTITY % heading "H1|H2|H3|H4|H5|H6">
<!ENTITY % list "UL | OL">
<!ENTITY % preformatted "PRE">
<!--================ Character mnemonic entities =========================-->
<!ENTITY % HTMLlat1 PUBLIC
"-//W3C//ENTITIES Latin1//EN//HTML"
"HTMLlat1.ent">
%HTMLlat1;
<!ENTITY % HTMLsymbol PUBLIC
"-//W3C//ENTITIES Symbols//EN//HTML"
"HTMLsymbol.ent">
%HTMLsymbol;
<!ENTITY % HTMLspecial PUBLIC
"-//W3C//ENTITIES Special//EN//HTML"
"HTMLspecial.ent">
%HTMLspecial;
<!--=================== Generic Attributes ===============================-->
<!ENTITY % coreattrs
"id ID #IMPLIED -- document-wide unique id --
class CDATA #IMPLIED -- space-separated list of classes --
style %StyleSheet; #IMPLIED -- associated style info --
title %Text; #IMPLIED -- advisory title --"
>
<!ENTITY % i18n
"lang %LanguageCode; #IMPLIED -- language code --
dir (ltr|rtl) #IMPLIED -- direction for weak/neutral text --"
>
<!ENTITY % events
"onclick %Script; #IMPLIED -- a pointer button was clicked --
ondblclick %Script; #IMPLIED -- a pointer button was double clicked--
onmousedown %Script; #IMPLIED -- a pointer button was pressed down --
onmouseup %Script; #IMPLIED -- a pointer button was released --
onmouseover %Script; #IMPLIED -- a pointer was moved onto --
onmousemove %Script; #IMPLIED -- a pointer was moved within --
onmouseout %Script; #IMPLIED -- a pointer was moved away --
onkeypress %Script; #IMPLIED -- a key was pressed and released --
onkeydown %Script; #IMPLIED -- a key was pressed down --
onkeyup %Script; #IMPLIED -- a key was released --"
>
<!-- Reserved Feature Switch -->
<!ENTITY % HTML.Reserved "IGNORE">
<!-- The following attributes are reserved for possible future use -->
<![ %HTML.Reserved; [
<!ENTITY % reserved
"datasrc %URI; #IMPLIED -- a single or tabular Data Source --
datafld CDATA #IMPLIED -- the property or column name --
dataformatas (plaintext|html) plaintext -- text or html --"
>
]]>
<!ENTITY % reserved "">
<!ENTITY % attrs "%coreattrs; %i18n; %events;">
<!--=================== Text Markup ======================================-->
<!ENTITY % fontstyle
"TT | I | B | BIG | SMALL">
<!ENTITY % phrase "EM | STRONG | DFN | CODE |
SAMP | KBD | VAR | CITE | ABBR | ACRONYM" >
<!ENTITY % special
"A | IMG | OBJECT | BR | SCRIPT | MAP | Q | SUB | SUP | SPAN | BDO">
<!ENTITY % formctrl "INPUT | SELECT | TEXTAREA | LABEL | BUTTON">
<!-- %inline; covers inline or "text-level" elements -->
<!ENTITY % inline "#PCDATA | %fontstyle; | %phrase; | %special; | %formctrl;">
<!ELEMENT (%fontstyle;|%phrase;) - - (%inline;)*>
<!ATTLIST (%fontstyle;|%phrase;)
%attrs; -- %coreattrs, %i18n, %events --
>
<!ELEMENT (SUB|SUP) - - (%inline;)* -- subscript, superscript -->
<!ATTLIST (SUB|SUP)
%attrs; -- %coreattrs, %i18n, %events --
>
<!ELEMENT SPAN - - (%inline;)* -- generic language/style container -->
<!ATTLIST SPAN
%attrs; -- %coreattrs, %i18n, %events --
%reserved; -- reserved for possible future use --
>
<!ELEMENT BDO - - (%inline;)* -- I18N BiDi over-ride -->
<!ATTLIST BDO
%coreattrs; -- id, class, style, title --
lang %LanguageCode; #IMPLIED -- language code --
dir (ltr|rtl) #REQUIRED -- directionality --
>
<!ELEMENT BR - O EMPTY -- forced line break -->
<!ATTLIST BR
%coreattrs; -- id, class, style, title --
>
<!--================== HTML content models ===============================-->
<!--
HTML has two basic content models:
%inline; character level elements and text strings
%block; block-like elements e.g. paragraphs and lists
-->
<!ENTITY % block
"P | %heading; | %list; | %preformatted; | DL | DIV | NOSCRIPT |
BLOCKQUOTE | FORM | HR | TABLE | FIELDSET | ADDRESS">
<!ENTITY % flow "%block; | %inline;">
<!--=================== Document Body ====================================-->
<!ELEMENT BODY O O (%block;|SCRIPT)+ +(INS|DEL) -- document body -->
<!ATTLIST BODY
%attrs; -- %coreattrs, %i18n, %events --
onload %Script; #IMPLIED -- the document has been loaded --
onunload %Script; #IMPLIED -- the document has been removed --
>
<!ELEMENT ADDRESS - - (%inline;)* -- information on author -->
<!ATTLIST ADDRESS
%attrs; -- %coreattrs, %i18n, %events --
>
<!ELEMENT DIV - - (%flow;)* -- generic language/style container -->
<!ATTLIST DIV
%attrs; -- %coreattrs, %i18n, %events --
%reserved; -- reserved for possible future use --
>
<!--================== The Anchor Element ================================-->
<!ENTITY % Shape "(rect|circle|poly|default)">
<!ENTITY % Coords "CDATA" -- comma-separated list of lengths -->
<!ELEMENT A - - (%inline;)* -(A) -- anchor -->
<!ATTLIST A
%attrs; -- %coreattrs, %i18n, %events --
charset %Charset; #IMPLIED -- char encoding of linked resource --
type %ContentType; #IMPLIED -- advisory content type --
name CDATA #IMPLIED -- named link end --
href %URI; #IMPLIED -- URI for linked resource --
hreflang %LanguageCode; #IMPLIED -- language code --
rel %LinkTypes; #IMPLIED -- forward link types --
rev %LinkTypes; #IMPLIED -- reverse link types --
accesskey %Character; #IMPLIED -- accessibility key character --
shape %Shape; rect -- for use with client-side image maps -
-
coords %Coords; #IMPLIED -- for use with client-side image maps -
-
tabindex NUMBER #IMPLIED -- position in tabbing order --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
>
<!--================== Client-side image maps ============================-->
<!-- These can be placed in the same document or grouped in a
separate document although this isn't yet widely supported -->
<!ELEMENT MAP - - ((%block;) | AREA)+ -- client-side image map -->
<!ATTLIST MAP
%attrs; -- %coreattrs, %i18n, %events --
name CDATA #REQUIRED -- for reference by usemap --
>
<!ELEMENT AREA - O EMPTY -- client-side image map area -->
<!ATTLIST AREA
%attrs; -- %coreattrs, %i18n, %events --
shape %Shape; rect -- controls interpretation of coords --
coords %Coords; #IMPLIED -- comma-separated list of lengths --
href %URI; #IMPLIED -- URI for linked resource --
nohref (nohref) #IMPLIED -- this region has no action --
alt %Text; #REQUIRED -- short description --
tabindex NUMBER #IMPLIED -- position in tabbing order --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
>
<!--================== The LINK Element ==================================-->
<!--
Relationship values can be used in principle:
a) for document specific toolbars/menus when used
with the LINK element in document head e.g.
start, contents, previous, next, index, end, help
b) to link to a separate style sheet (rel=stylesheet)
c) to make a link to a script (rel=script)
d) by stylesheets to control how collections of
html nodes are rendered into printed documents
e) to make a link to a printable version of this document
e.g. a postscript or pdf version (rel=alternate media=print)
-->
<!ELEMENT LINK - O EMPTY -- a media-independent link -->
<!ATTLIST LINK
%attrs; -- %coreattrs, %i18n, %events --
charset %Charset; #IMPLIED -- char encoding of linked resource --
href %URI; #IMPLIED -- URI for linked resource --
hreflang %LanguageCode; #IMPLIED -- language code --
type %ContentType; #IMPLIED -- advisory content type --
rel %LinkTypes; #IMPLIED -- forward link types --
rev %LinkTypes; #IMPLIED -- reverse link types --
media %MediaDesc; #IMPLIED -- for rendering on these media --
>
<!--=================== Images ===========================================-->
<!-- Length defined in strict DTD for cellpadding/cellspacing -->
<!ENTITY % Length "CDATA" -- nn for pixels or nn% for percentage length -->
<!ENTITY % MultiLength "CDATA" -- pixel, percentage, or relative -->
<![ %HTML.Frameset; [
<!ENTITY % MultiLengths "CDATA" -- comma-separated list of MultiLength -->
]]>
<!ENTITY % Pixels "CDATA" -- integer representing length in pixels -->
<!-- To avoid problems with text-only UAs as well as
to make image content understandable and navigable
to users of non-visual UAs, you need to provide
a description with ALT, and avoid server-side image maps -->
<!ELEMENT IMG - O EMPTY -- Embedded image -->
<!ATTLIST IMG
%attrs; -- %coreattrs, %i18n, %events --
src %URI; #REQUIRED -- URI of image to embed --
alt %Text; #REQUIRED -- short description --
longdesc %URI; #IMPLIED -- link to long description
(complements alt) --
name CDATA #IMPLIED -- name of image for scripting --
height %Length; #IMPLIED -- override height --
width %Length; #IMPLIED -- override width --
usemap %URI; #IMPLIED -- use client-side image map --
ismap (ismap) #IMPLIED -- use server-side image map --
>
<!-- USEMAP points to a MAP element which may be in this document
or an external document, although the latter is not widely supported -->
<!--==================== OBJECT ======================================-->
<!--
OBJECT is used to embed objects as part of HTML pages
PARAM elements should precede other content. SGML mixed content
model technicality precludes specifying this formally ...
-->
<!ELEMENT OBJECT - - (PARAM | %flow;)*
-- generic embedded object -->
<!ATTLIST OBJECT
%attrs; -- %coreattrs, %i18n, %events --
declare (declare) #IMPLIED -- declare but don't instantiate flag --
classid %URI; #IMPLIED -- identifies an implementation --
codebase %URI; #IMPLIED -- base URI for classid, data, archive--
data %URI; #IMPLIED -- reference to object's data --
type %ContentType; #IMPLIED -- content type for data --
codetype %ContentType; #IMPLIED -- content type for code --
archive CDATA #IMPLIED -- space-separated list of URIs --
standby %Text; #IMPLIED -- message to show while loading --
height %Length; #IMPLIED -- override height --
width %Length; #IMPLIED -- override width --
usemap %URI; #IMPLIED -- use client-side image map --
name CDATA #IMPLIED -- submit as part of form --
tabindex NUMBER #IMPLIED -- position in tabbing order --
%reserved; -- reserved for possible future use --
>
<!ELEMENT PARAM - O EMPTY -- named property value -->
<!ATTLIST PARAM
id ID #IMPLIED -- document-wide unique id --
name CDATA #REQUIRED -- property name --
value CDATA #IMPLIED -- property value --
valuetype (DATA|REF|OBJECT) DATA -- How to interpret value --
type %ContentType; #IMPLIED -- content type for value
when valuetype=ref --
>
<!--=================== Horizontal Rule ==================================-->
<!ELEMENT HR - O EMPTY -- horizontal rule -->
<!ATTLIST HR
%attrs; -- %coreattrs, %i18n, %events --
>
<!--=================== Paragraphs =======================================-->
<!ELEMENT P - O (%inline;)* -- paragraph -->
<!ATTLIST P
%attrs; -- %coreattrs, %i18n, %events --
>
<!--=================== Headings =========================================-->
<!--
There are six levels of headings from H1 (the most important)
to H6 (the least important).
-->
<!ELEMENT (%heading;) - - (%inline;)* -- heading -->
<!ATTLIST (%heading;)
%attrs; -- %coreattrs, %i18n, %events --
>
<!--=================== Preformatted Text ================================-->
<!-- excludes markup for images and changes in font size -->
<!ENTITY % pre.exclusion "IMG|OBJECT|BIG|SMALL|SUB|SUP">
<!ELEMENT PRE - - (%inline;)* -(%pre.exclusion;) -- preformatted text -->
<!ATTLIST PRE
%attrs; -- %coreattrs, %i18n, %events --
>
<!--===================== Inline Quotes ==================================-->
<!ELEMENT Q - - (%inline;)* -- short inline quotation -->
<!ATTLIST Q
%attrs; -- %coreattrs, %i18n, %events --
cite %URI; #IMPLIED -- URI for source document or msg --
>
<!--=================== Block-like Quotes ================================-->
<!ELEMENT BLOCKQUOTE - - (%block;|SCRIPT)+ -- long quotation -->
<!ATTLIST BLOCKQUOTE
%attrs; -- %coreattrs, %i18n, %events --
cite %URI; #IMPLIED -- URI for source document or msg --
>
<!--=================== Inserted/Deleted Text ============================-->
<!-- INS/DEL are handled by inclusion on BODY -->
<!ELEMENT (INS|DEL) - - (%flow;)* -- inserted text, deleted text -->
<!ATTLIST (INS|DEL)
%attrs; -- %coreattrs, %i18n, %events --
cite %URI; #IMPLIED -- info on reason for change --
datetime %Datetime; #IMPLIED -- date and time of change --
>
<!--=================== Lists ============================================-->
<!-- definition lists - DT for term, DD for its definition -->
<!ELEMENT DL - - (DT|DD)+ -- definition list -->
<!ATTLIST DL
%attrs; -- %coreattrs, %i18n, %events --
>
<!ELEMENT DT - O (%inline;)* -- definition term -->
<!ELEMENT DD - O (%flow;)* -- definition description -->
<!ATTLIST (DT|DD)
%attrs; -- %coreattrs, %i18n, %events --
>
<!ELEMENT OL - - (LI)+ -- ordered list -->
<!ATTLIST OL
%attrs; -- %coreattrs, %i18n, %events --
>
<!-- Unordered Lists (UL) bullet styles -->
<!ELEMENT UL - - (LI)+ -- unordered list -->
<!ATTLIST UL
%attrs; -- %coreattrs, %i18n, %events --
>
<!ELEMENT LI - O (%flow;)* -- list item -->
<!ATTLIST LI
%attrs; -- %coreattrs, %i18n, %events --
>
<!--================ Forms ===============================================-->
<!ELEMENT FORM - - (%block;|SCRIPT)+ -(FORM) -- interactive form -->
<!ATTLIST FORM
%attrs; -- %coreattrs, %i18n, %events --
action %URI; #REQUIRED -- server-side form handler --
method (GET|POST) GET -- HTTP method used to submit the form--
enctype %ContentType; "application/x-www-form-urlencoded"
accept %ContentTypes; #IMPLIED -- list of MIME types for file upload --
name CDATA #IMPLIED -- name of form for scripting --
onsubmit %Script; #IMPLIED -- the form was submitted --
onreset %Script; #IMPLIED -- the form was reset --
accept-charset %Charsets; #IMPLIED -- list of supported charsets --
>
<!-- Each label must not contain more than ONE field -->
<!ELEMENT LABEL - - (%inline;)* -(LABEL) -- form field label text -->
<!ATTLIST LABEL
%attrs; -- %coreattrs, %i18n, %events --
for IDREF #IMPLIED -- matches field ID value --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
>
<!ENTITY % InputType
"(TEXT | PASSWORD | CHECKBOX |
RADIO | SUBMIT | RESET |
FILE | HIDDEN | IMAGE | BUTTON)"
>
<!-- attribute name required for all but submit and reset -->
<!ELEMENT INPUT - O EMPTY -- form control -->
<!ATTLIST INPUT
%attrs; -- %coreattrs, %i18n, %events --
type %InputType; TEXT -- what kind of widget is needed --
name CDATA #IMPLIED -- submit as part of form --
value CDATA #IMPLIED -- Specify for radio buttons and checkbo
xes --
checked (checked) #IMPLIED -- for radio buttons and check boxes --
disabled (disabled) #IMPLIED -- unavailable in this context --
readonly (readonly) #IMPLIED -- for text and passwd --
size CDATA #IMPLIED -- specific to each type of field --
maxlength NUMBER #IMPLIED -- max chars for text fields --
src %URI; #IMPLIED -- for fields with images --
alt CDATA #IMPLIED -- short description --
usemap %URI; #IMPLIED -- use client-side image map --
ismap (ismap) #IMPLIED -- use server-side image map --
tabindex NUMBER #IMPLIED -- position in tabbing order --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
onselect %Script; #IMPLIED -- some text was selected --
onchange %Script; #IMPLIED -- the element value was changed --
accept %ContentTypes; #IMPLIED -- list of MIME types for file upload --
%reserved; -- reserved for possible future use --
>
<!ELEMENT SELECT - - (OPTGROUP|OPTION)+ -- option selector -->
<!ATTLIST SELECT
%attrs; -- %coreattrs, %i18n, %events --
name CDATA #IMPLIED -- field name --
size NUMBER #IMPLIED -- rows visible --
multiple (multiple) #IMPLIED -- default is single selection --
disabled (disabled) #IMPLIED -- unavailable in this context --
tabindex NUMBER #IMPLIED -- position in tabbing order --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
onchange %Script; #IMPLIED -- the element value was changed --
%reserved; -- reserved for possible future use --
>
<!ELEMENT OPTGROUP - - (OPTION)+ -- option group -->
<!ATTLIST OPTGROUP
%attrs; -- %coreattrs, %i18n, %events --
disabled (disabled) #IMPLIED -- unavailable in this context --
label %Text; #REQUIRED -- for use in hierarchical menus --
>
<!ELEMENT OPTION - O (#PCDATA) -- selectable choice -->
<!ATTLIST OPTION
%attrs; -- %coreattrs, %i18n, %events --
selected (selected) #IMPLIED
disabled (disabled) #IMPLIED -- unavailable in this context --
label %Text; #IMPLIED -- for use in hierarchical menus --
value CDATA #IMPLIED -- defaults to element content --
>
<!ELEMENT TEXTAREA - - (#PCDATA) -- multi-line text field -->
<!ATTLIST TEXTAREA
%attrs; -- %coreattrs, %i18n, %events --
name CDATA #IMPLIED
rows NUMBER #REQUIRED
cols NUMBER #REQUIRED
disabled (disabled) #IMPLIED -- unavailable in this context --
readonly (readonly) #IMPLIED
tabindex NUMBER #IMPLIED -- position in tabbing order --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
onselect %Script; #IMPLIED -- some text was selected --
onchange %Script; #IMPLIED -- the element value was changed --
%reserved; -- reserved for possible future use --
>
<!--
#PCDATA is to solve the mixed content problem,
per specification only whitespace is allowed there!
-->
<!ELEMENT FIELDSET - - (#PCDATA,LEGEND,(%flow;)*) -- form control group -->
<!ATTLIST FIELDSET
%attrs; -- %coreattrs, %i18n, %events --
>
<!ELEMENT LEGEND - - (%inline;)* -- fieldset legend -->
<!ATTLIST LEGEND
%attrs; -- %coreattrs, %i18n, %events --
accesskey %Character; #IMPLIED -- accessibility key character --
>
<!ELEMENT BUTTON - -
(%flow;)* -(A|%formctrl;|FORM|FIELDSET)
-- push button -->
<!ATTLIST BUTTON
%attrs; -- %coreattrs, %i18n, %events --
name CDATA #IMPLIED
value CDATA #IMPLIED -- sent to server when submitted --
type (button|submit|reset) submit -- for use as form button --
disabled (disabled) #IMPLIED -- unavailable in this context --
tabindex NUMBER #IMPLIED -- position in tabbing order --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
%reserved; -- reserved for possible future use --
>
<!--======================= Tables =======================================-->
<!-- IETF HTML table standard, see [RFC1942] -->
<!--
The BORDER attribute sets the thickness of the frame around the
table. The default units are screen pixels.
The FRAME attribute specifies which parts of the frame around
the table should be rendered. The values are not the same as
CALS to avoid a name clash with the VALIGN attribute.
The value "border" is included for backwards compatibility with
<TABLE BORDER> which yields frame=border and border=implied
For <TABLE BORDER=1> you get border=1 and frame=implied. In this
case, it is appropriate to treat this as frame=border for backwards
compatibility with deployed browsers.
-->
<!ENTITY % TFrame "(void|above|below|hsides|lhs|rhs|vsides|box|border)">
<!--
The RULES attribute defines which rules to draw between cells:
If RULES is absent then assume:
"none" if BORDER is absent or BORDER=0 otherwise "all"
-->
<!ENTITY % TRules "(none | groups | rows | cols | all)">
<!-- horizontal placement of table relative to document -->
<!ENTITY % TAlign "(left|center|right)">
<!-- horizontal alignment attributes for cell contents -->
<!ENTITY % cellhalign
"align (left|center|right|justify|char) #IMPLIED
char %Character; #IMPLIED -- alignment char, e.g. char=':' --
charoff %Length; #IMPLIED -- offset for alignment char --"
>
<!-- vertical alignment attributes for cell contents -->
<!ENTITY % cellvalign
"valign (top|middle|bottom|baseline) #IMPLIED"
>
<!ELEMENT TABLE - -
(CAPTION?, (COL*|COLGROUP*), THEAD?, TFOOT?, TBODY+)>
<!ELEMENT CAPTION - - (%inline;)* -- table caption -->
<!ELEMENT THEAD - O (TR)+ -- table header -->
<!ELEMENT TFOOT - O (TR)+ -- table footer -->
<!ELEMENT TBODY O O (TR)+ -- table body -->
<!ELEMENT COLGROUP - O (COL)* -- table column group -->
<!ELEMENT COL - O EMPTY -- table column -->
<!ELEMENT TR - O (TH|TD)+ -- table row -->
<!ELEMENT (TH|TD) - O (%flow;)* -- table header cell, table data cell-->
<!ATTLIST TABLE -- table element --
%attrs; -- %coreattrs, %i18n, %events --
summary %Text; #IMPLIED -- purpose/structure for speech output--
width %Length; #IMPLIED -- table width --
border %Pixels; #IMPLIED -- controls frame width around table --
frame %TFrame; #IMPLIED -- which parts of frame to render --
rules %TRules; #IMPLIED -- rulings between rows and cols --
cellspacing %Length; #IMPLIED -- spacing between cells --
cellpadding %Length; #IMPLIED -- spacing within cells --
%reserved; -- reserved for possible future use --
datapagesize CDATA #IMPLIED -- reserved for possible future use --
>
<!ATTLIST CAPTION
%attrs; -- %coreattrs, %i18n, %events --
>
<!--
COLGROUP groups a set of COL elements. It allows you to group
several semantically related columns together.
-->
<!ATTLIST COLGROUP
%attrs; -- %coreattrs, %i18n, %events --
span NUMBER 1 -- default number of columns in group --
width %MultiLength; #IMPLIED -- default width for enclosed COLs --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
>
<!--
COL elements define the alignment properties for cells in
one or more columns.
The WIDTH attribute specifies the width of the columns, e.g.
width=64 width in screen pixels
width=0.5* relative width of 0.5
The SPAN attribute causes the attributes of one
COL element to apply to more than one column.
-->
<!ATTLIST COL -- column groups and properties --
%attrs; -- %coreattrs, %i18n, %events --
span NUMBER 1 -- COL attributes affect N columns --
width %MultiLength; #IMPLIED -- column width specification --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
>
<!--
Use THEAD to duplicate headers when breaking table
across page boundaries, or for static headers when
TBODY sections are rendered in scrolling panel.
Use TFOOT to duplicate footers when breaking table
across page boundaries, or for static footers when
TBODY sections are rendered in scrolling panel.
Use multiple TBODY sections when rules are needed
between groups of table rows.
-->
<!ATTLIST (THEAD|TBODY|TFOOT) -- table section --
%attrs; -- %coreattrs, %i18n, %events --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
>
<!ATTLIST TR -- table row --
%attrs; -- %coreattrs, %i18n, %events --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
>
<!-- Scope is simpler than headers attribute for common tables -->
<!ENTITY % Scope "(row|col|rowgroup|colgroup)">
<!-- TH is for headers, TD for data, but for cells acting as both use TD -->
<!ATTLIST (TH|TD) -- header or data cell --
%attrs; -- %coreattrs, %i18n, %events --
abbr %Text; #IMPLIED -- abbreviation for header cell --
axis CDATA #IMPLIED -- comma-separated list of related heade
rs--
headers IDREFS #IMPLIED -- list of id's for header cells --
scope %Scope; #IMPLIED -- scope covered by header cells --
rowspan NUMBER 1 -- number of rows spanned by cell --
colspan NUMBER 1 -- number of cols spanned by cell --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
>
<!--================ Document Head =======================================-->
<!-- %head.misc; defined earlier on as "SCRIPT|STYLE|META|LINK|OBJECT" -->
<!ENTITY % head.content "TITLE & BASE?">
<!ELEMENT HEAD O O (%head.content;) +(%head.misc;) -- document head -->
<!ATTLIST HEAD
%i18n; -- lang, dir --
profile %URI; #IMPLIED -- named dictionary of meta info --
>
<!-- The TITLE element is not considered part of the flow of text.
It should be displayed, for example as the page header or
window title. Exactly one title is required per document.
-->
<!ELEMENT TITLE - - (#PCDATA) -(%head.misc;) -- document title -->
<!ATTLIST TITLE %i18n>
<!ELEMENT BASE - O EMPTY -- document base URI -->
<!ATTLIST BASE
href %URI; #REQUIRED -- URI that acts as base URI --
>
<!ELEMENT META - O EMPTY -- generic metainformation -->
<!ATTLIST META
%i18n; -- lang, dir, for use with content --
http-equiv NAME #IMPLIED -- HTTP response header name --
name NAME #IMPLIED -- metainformation name --
content CDATA #REQUIRED -- associated information --
scheme CDATA #IMPLIED -- select form of content --
>
<!ELEMENT STYLE - - %StyleSheet -- style info -->
<!ATTLIST STYLE
%i18n; -- lang, dir, for use with title --
type %ContentType; #REQUIRED -- content type of style language --
media %MediaDesc; #IMPLIED -- designed for use with these media --
title %Text; #IMPLIED -- advisory title --
>
<!ELEMENT SCRIPT - - %Script; -- script statements -->
<!ATTLIST SCRIPT
charset %Charset; #IMPLIED -- char encoding of linked resource --
type %ContentType; #REQUIRED -- content type of script language --
src %URI; #IMPLIED -- URI for an external script --
defer (defer) #IMPLIED -- UA may defer execution of script --
event CDATA #IMPLIED -- reserved for possible future use --
for %URI; #IMPLIED -- reserved for possible future use --
>
<!ELEMENT NOSCRIPT - - (%block;)+
-- alternate content container for non script-based rendering -->
<!ATTLIST NOSCRIPT
%attrs; -- %coreattrs, %i18n, %events --
>
<!--================ Document Structure ==================================-->
<!ENTITY % html.content "HEAD, BODY">
<!ELEMENT HTML O O (%html.content;) -- document root element -->
<!ATTLIST HTML
%i18n; -- lang, dir --
>
22 Transitional Document Type Definition
<!--
This is the HTML 4.01 Transitional DTD, which includes
presentation attributes and elements that W3C expects to phase out
as support for style sheets matures. Authors should use the Strict
DTD when possible, but may use the Transitional DTD when support
for presentation attribute and elements is required.
HTML 4 includes mechanisms for style sheets, scripting,
embedding objects, improved support for right to left and mixed
direction text, and enhancements to forms for improved
accessibility for people with disabilities.
Draft: $Date: 1999/12/24 23:37:46 $
Authors:
Dave Raggett <dsr@w3.org>
Arnaud Le Hors <lehors@w3.org>
Ian Jacobs <ij@w3.org>
Further information about HTML 4.01 is available at:
http://www.w3.org/TR/1999/REC-html401-19991224
The HTML 4.01 specification includes additional
syntactic constraints that cannot be expressed within
the DTDs.
-->
<!ENTITY % HTML.Version "-//W3C//DTD HTML 4.01 Transitional//EN"
-- Typical usage:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
...
</head>
<body>
...
</body>
</html>
The URI used as a system identifier with the public identifier allows
the user agent to download the DTD and entity sets as needed.
The FPI for the Strict HTML 4.01 DTD is:
"-//W3C//DTD HTML 4.01//EN"
This version of the strict DTD is:
http://www.w3.org/TR/1999/REC-html401-19991224/strict.dtd
Authors should use the Strict DTD unless they need the
presentation control for user agents that don't (adequately)
support style sheets.
If you are writing a document that includes frames, use
the following FPI:
"-//W3C//DTD HTML 4.01 Frameset//EN"
This version of the frameset DTD is:
http://www.w3.org/TR/1999/REC-html401-19991224/frameset.dtd
Use the following (relative) URIs to refer to
the DTDs and entity definitions of this specification:
"strict.dtd"
"loose.dtd"
"frameset.dtd"
"HTMLlat1.ent"
"HTMLsymbol.ent"
"HTMLspecial.ent"
-->
<!--================== Imported Names ====================================-->
<!-- Feature Switch for frameset documents -->
<!ENTITY % HTML.Frameset "IGNORE">
<!ENTITY % ContentType "CDATA"
-- media type, as per [RFC2045]
-->
<!ENTITY % ContentTypes "CDATA"
-- comma-separated list of media types, as per [RFC2045]
-->
<!ENTITY % Charset "CDATA"
-- a character encoding, as per [RFC2045]
-->
<!ENTITY % Charsets "CDATA"
-- a space-separated list of character encodings, as per [RFC2045]
-->
<!ENTITY % LanguageCode "NAME"
-- a language code, as per [RFC1766]
-->
<!ENTITY % Character "CDATA"
-- a single character from [ISO10646]
-->
<!ENTITY % LinkTypes "CDATA"
-- space-separated list of link types
-->
<!ENTITY % MediaDesc "CDATA"
-- single or comma-separated list of media descriptors
-->
<!ENTITY % URI "CDATA"
-- a Uniform Resource Identifier,
see [URI]
-->
<!ENTITY % Datetime "CDATA" -- date and time information. ISO date format -->
<!ENTITY % Script "CDATA" -- script expression -->
<!ENTITY % StyleSheet "CDATA" -- style sheet data -->
<!ENTITY % FrameTarget "CDATA" -- render in this frame -->
<!ENTITY % Text "CDATA">
<!-- Parameter Entities -->
<!ENTITY % head.misc "SCRIPT|STYLE|META|LINK|OBJECT" -- repeatable head element
s -->
<!ENTITY % heading "H1|H2|H3|H4|H5|H6">
<!ENTITY % list "UL | OL | DIR | MENU">
<!ENTITY % preformatted "PRE">
<!ENTITY % Color "CDATA" -- a color using sRGB: #RRGGBB as Hex values -->
<!-- There are also 16 widely known color names with their sRGB values:
Black = #000000 Green = #008000
Silver = #C0C0C0 Lime = #00FF00
Gray = #808080 Olive = #808000
White = #FFFFFF Yellow = #FFFF00
Maroon = #800000 Navy = #000080
Red = #FF0000 Blue = #0000FF
Purple = #800080 Teal = #008080
Fuchsia= #FF00FF Aqua = #00FFFF
-->
<!ENTITY % bodycolors "
bgcolor %Color; #IMPLIED -- document background color --
text %Color; #IMPLIED -- document text color --
link %Color; #IMPLIED -- color of links --
vlink %Color; #IMPLIED -- color of visited links --
alink %Color; #IMPLIED -- color of selected links --
">
<!--================ Character mnemonic entities =========================-->
<!ENTITY % HTMLlat1 PUBLIC
"-//W3C//ENTITIES Latin1//EN//HTML"
"HTMLlat1.ent">
%HTMLlat1;
<!ENTITY % HTMLsymbol PUBLIC
"-//W3C//ENTITIES Symbols//EN//HTML"
"HTMLsymbol.ent">
%HTMLsymbol;
<!ENTITY % HTMLspecial PUBLIC
"-//W3C//ENTITIES Special//EN//HTML"
"HTMLspecial.ent">
%HTMLspecial;
<!--=================== Generic Attributes ===============================-->
<!ENTITY % coreattrs
"id ID #IMPLIED -- document-wide unique id --
class CDATA #IMPLIED -- space-separated list of classes --
style %StyleSheet; #IMPLIED -- associated style info --
title %Text; #IMPLIED -- advisory title --"
>
<!ENTITY % i18n
"lang %LanguageCode; #IMPLIED -- language code --
dir (ltr|rtl) #IMPLIED -- direction for weak/neutral text --"
>
<!ENTITY % events
"onclick %Script; #IMPLIED -- a pointer button was clicked --
ondblclick %Script; #IMPLIED -- a pointer button was double clicked--
onmousedown %Script; #IMPLIED -- a pointer button was pressed down --
onmouseup %Script; #IMPLIED -- a pointer button was released --
onmouseover %Script; #IMPLIED -- a pointer was moved onto --
onmousemove %Script; #IMPLIED -- a pointer was moved within --
onmouseout %Script; #IMPLIED -- a pointer was moved away --
onkeypress %Script; #IMPLIED -- a key was pressed and released --
onkeydown %Script; #IMPLIED -- a key was pressed down --
onkeyup %Script; #IMPLIED -- a key was released --"
>
<!-- Reserved Feature Switch -->
<!ENTITY % HTML.Reserved "IGNORE">
<!-- The following attributes are reserved for possible future use -->
<![ %HTML.Reserved; [
<!ENTITY % reserved
"datasrc %URI; #IMPLIED -- a single or tabular Data Source --
datafld CDATA #IMPLIED -- the property or column name --
dataformatas (plaintext|html) plaintext -- text or html --"
>
]]>
<!ENTITY % reserved "">
<!ENTITY % attrs "%coreattrs; %i18n; %events;">
<!ENTITY % align "align (left|center|right|justify) #IMPLIED"
-- default is left for ltr paragraphs, right for rtl --
>
<!--=================== Text Markup ======================================-->
<!ENTITY % fontstyle
"TT | I | B | U | S | STRIKE | BIG | SMALL">
<!ENTITY % phrase "EM | STRONG | DFN | CODE |
SAMP | KBD | VAR | CITE | ABBR | ACRONYM" >
<!ENTITY % special
"A | IMG | APPLET | OBJECT | FONT | BASEFONT | BR | SCRIPT |
MAP | Q | SUB | SUP | SPAN | BDO | IFRAME">
<!ENTITY % formctrl "INPUT | SELECT | TEXTAREA | LABEL | BUTTON">
<!-- %inline; covers inline or "text-level" elements -->
<!ENTITY % inline "#PCDATA | %fontstyle; | %phrase; | %special; | %formctrl;">
<!ELEMENT (%fontstyle;|%phrase;) - - (%inline;)*>
<!ATTLIST (%fontstyle;|%phrase;)
%attrs; -- %coreattrs, %i18n, %events --
>
<!ELEMENT (SUB|SUP) - - (%inline;)* -- subscript, superscript -->
<!ATTLIST (SUB|SUP)
%attrs; -- %coreattrs, %i18n, %events --
>
<!ELEMENT SPAN - - (%inline;)* -- generic language/style container -->
<!ATTLIST SPAN
%attrs; -- %coreattrs, %i18n, %events --
%reserved; -- reserved for possible future use --
>
<!ELEMENT BDO - - (%inline;)* -- I18N BiDi over-ride -->
<!ATTLIST BDO
%coreattrs; -- id, class, style, title --
lang %LanguageCode; #IMPLIED -- language code --
dir (ltr|rtl) #REQUIRED -- directionality --
>
<!ELEMENT BASEFONT - O EMPTY -- base font size -->
<!ATTLIST BASEFONT
id ID #IMPLIED -- document-wide unique id --
size CDATA #REQUIRED -- base font size for FONT elements --
color %Color; #IMPLIED -- text color --
face CDATA #IMPLIED -- comma-separated list of font names --
>
<!ELEMENT FONT - - (%inline;)* -- local change to font -->
<!ATTLIST FONT
%coreattrs; -- id, class, style, title --
%i18n; -- lang, dir --
size CDATA #IMPLIED -- [+|-]nn e.g. size="+1", size="4" --
color %Color; #IMPLIED -- text color --
face CDATA #IMPLIED -- comma-separated list of font names --
>
<!ELEMENT BR - O EMPTY -- forced line break -->
<!ATTLIST BR
%coreattrs; -- id, class, style, title --
clear (left|all|right|none) none -- control of text flow --
>
<!--================== HTML content models ===============================-->
<!--
HTML has two basic content models:
%inline; character level elements and text strings
%block; block-like elements e.g. paragraphs and lists
-->
<!ENTITY % block
"P | %heading; | %list; | %preformatted; | DL | DIV | CENTER |
NOSCRIPT | NOFRAMES | BLOCKQUOTE | FORM | ISINDEX | HR |
TABLE | FIELDSET | ADDRESS">
<!ENTITY % flow "%block; | %inline;">
<!--=================== Document Body ====================================-->
<!ELEMENT BODY O O (%flow;)* +(INS|DEL) -- document body -->
<!ATTLIST BODY
%attrs; -- %coreattrs, %i18n, %events --
onload %Script; #IMPLIED -- the document has been loaded --
onunload %Script; #IMPLIED -- the document has been removed --
background %URI; #IMPLIED -- texture tile for document
background --
%bodycolors; -- bgcolor, text, link, vlink, alink --
>
<!ELEMENT ADDRESS - - ((%inline;)|P)* -- information on author -->
<!ATTLIST ADDRESS
%attrs; -- %coreattrs, %i18n, %events --
>
<!ELEMENT DIV - - (%flow;)* -- generic language/style container -->
<!ATTLIST DIV
%attrs; -- %coreattrs, %i18n, %events --
%align; -- align, text alignment --
%reserved; -- reserved for possible future use --
>
<!ELEMENT CENTER - - (%flow;)* -- shorthand for DIV align=center -->
<!ATTLIST CENTER
%attrs; -- %coreattrs, %i18n, %events --
>
<!--================== The Anchor Element ================================-->
<!ENTITY % Shape "(rect|circle|poly|default)">
<!ENTITY % Coords "CDATA" -- comma-separated list of lengths -->
<!ELEMENT A - - (%inline;)* -(A) -- anchor -->
<!ATTLIST A
%attrs; -- %coreattrs, %i18n, %events --
charset %Charset; #IMPLIED -- char encoding of linked resource --
type %ContentType; #IMPLIED -- advisory content type --
name CDATA #IMPLIED -- named link end --
href %URI; #IMPLIED -- URI for linked resource --
hreflang %LanguageCode; #IMPLIED -- language code --
target %FrameTarget; #IMPLIED -- render in this frame --
rel %LinkTypes; #IMPLIED -- forward link types --
rev %LinkTypes; #IMPLIED -- reverse link types --
accesskey %Character; #IMPLIED -- accessibility key character --
shape %Shape; rect -- for use with client-side image maps -
-
coords %Coords; #IMPLIED -- for use with client-side image maps -
-
tabindex NUMBER #IMPLIED -- position in tabbing order --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
>
<!--================== Client-side image maps ============================-->
<!-- These can be placed in the same document or grouped in a
separate document although this isn't yet widely supported -->
<!ELEMENT MAP - - ((%block;) | AREA)+ -- client-side image map -->
<!ATTLIST MAP
%attrs; -- %coreattrs, %i18n, %events --
name CDATA #REQUIRED -- for reference by usemap --
>
<!ELEMENT AREA - O EMPTY -- client-side image map area -->
<!ATTLIST AREA
%attrs; -- %coreattrs, %i18n, %events --
shape %Shape; rect -- controls interpretation of coords --
coords %Coords; #IMPLIED -- comma-separated list of lengths --
href %URI; #IMPLIED -- URI for linked resource --
target %FrameTarget; #IMPLIED -- render in this frame --
nohref (nohref) #IMPLIED -- this region has no action --
alt %Text; #REQUIRED -- short description --
tabindex NUMBER #IMPLIED -- position in tabbing order --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
>
<!--================== The LINK Element ==================================-->
<!--
Relationship values can be used in principle:
a) for document specific toolbars/menus when used
with the LINK element in document head e.g.
start, contents, previous, next, index, end, help
b) to link to a separate style sheet (rel=stylesheet)
c) to make a link to a script (rel=script)
d) by stylesheets to control how collections of
html nodes are rendered into printed documents
e) to make a link to a printable version of this document
e.g. a postscript or pdf version (rel=alternate media=print)
-->
<!ELEMENT LINK - O EMPTY -- a media-independent link -->
<!ATTLIST LINK
%attrs; -- %coreattrs, %i18n, %events --
charset %Charset; #IMPLIED -- char encoding of linked resource --
href %URI; #IMPLIED -- URI for linked resource --
hreflang %LanguageCode; #IMPLIED -- language code --
type %ContentType; #IMPLIED -- advisory content type --
rel %LinkTypes; #IMPLIED -- forward link types --
rev %LinkTypes; #IMPLIED -- reverse link types --
media %MediaDesc; #IMPLIED -- for rendering on these media --
target %FrameTarget; #IMPLIED -- render in this frame --
>
<!--=================== Images ===========================================-->
<!-- Length defined in strict DTD for cellpadding/cellspacing -->
<!ENTITY % Length "CDATA" -- nn for pixels or nn% for percentage length -->
<!ENTITY % MultiLength "CDATA" -- pixel, percentage, or relative -->
<![ %HTML.Frameset; [
<!ENTITY % MultiLengths "CDATA" -- comma-separated list of MultiLength -->
]]>
<!ENTITY % Pixels "CDATA" -- integer representing length in pixels -->
<!ENTITY % IAlign "(top|middle|bottom|left|right)" -- center? -->
<!-- To avoid problems with text-only UAs as well as
to make image content understandable and navigable
to users of non-visual UAs, you need to provide
a description with ALT, and avoid server-side image maps -->
<!ELEMENT IMG - O EMPTY -- Embedded image -->
<!ATTLIST IMG
%attrs; -- %coreattrs, %i18n, %events --
src %URI; #REQUIRED -- URI of image to embed --
alt %Text; #REQUIRED -- short description --
longdesc %URI; #IMPLIED -- link to long description
(complements alt) --
name CDATA #IMPLIED -- name of image for scripting --
height %Length; #IMPLIED -- override height --
width %Length; #IMPLIED -- override width --
usemap %URI; #IMPLIED -- use client-side image map --
ismap (ismap) #IMPLIED -- use server-side image map --
align %IAlign; #IMPLIED -- vertical or horizontal alignment --
border %Pixels; #IMPLIED -- link border width --
hspace %Pixels; #IMPLIED -- horizontal gutter --
vspace %Pixels; #IMPLIED -- vertical gutter --
>
<!-- USEMAP points to a MAP element which may be in this document
or an external document, although the latter is not widely supported -->
<!--==================== OBJECT ======================================-->
<!--
OBJECT is used to embed objects as part of HTML pages
PARAM elements should precede other content. SGML mixed content
model technicality precludes specifying this formally ...
-->
<!ELEMENT OBJECT - - (PARAM | %flow;)*
-- generic embedded object -->
<!ATTLIST OBJECT
%attrs; -- %coreattrs, %i18n, %events --
declare (declare) #IMPLIED -- declare but don't instantiate flag --
classid %URI; #IMPLIED -- identifies an implementation --
codebase %URI; #IMPLIED -- base URI for classid, data, archive--
data %URI; #IMPLIED -- reference to object's data --
type %ContentType; #IMPLIED -- content type for data --
codetype %ContentType; #IMPLIED -- content type for code --
archive CDATA #IMPLIED -- space-separated list of URIs --
standby %Text; #IMPLIED -- message to show while loading --
height %Length; #IMPLIED -- override height --
width %Length; #IMPLIED -- override width --
usemap %URI; #IMPLIED -- use client-side image map --
name CDATA #IMPLIED -- submit as part of form --
tabindex NUMBER #IMPLIED -- position in tabbing order --
align %IAlign; #IMPLIED -- vertical or horizontal alignment --
border %Pixels; #IMPLIED -- link border width --
hspace %Pixels; #IMPLIED -- horizontal gutter --
vspace %Pixels; #IMPLIED -- vertical gutter --
%reserved; -- reserved for possible future use --
>
<!ELEMENT PARAM - O EMPTY -- named property value -->
<!ATTLIST PARAM
id ID #IMPLIED -- document-wide unique id --
name CDATA #REQUIRED -- property name --
value CDATA #IMPLIED -- property value --
valuetype (DATA|REF|OBJECT) DATA -- How to interpret value --
type %ContentType; #IMPLIED -- content type for value
when valuetype=ref --
>
<!--=================== Java APPLET ==================================-->
<!--
One of code or object attributes must be present.
Place PARAM elements before other content.
-->
<!ELEMENT APPLET - - (PARAM | %flow;)* -- Java applet -->
<!ATTLIST APPLET
%coreattrs; -- id, class, style, title --
codebase %URI; #IMPLIED -- optional base URI for applet --
archive CDATA #IMPLIED -- comma-separated archive list --
code CDATA #IMPLIED -- applet class file --
object CDATA #IMPLIED -- serialized applet file --
alt %Text; #IMPLIED -- short description --
name CDATA #IMPLIED -- allows applets to find each other --
width %Length; #REQUIRED -- initial width --
height %Length; #REQUIRED -- initial height --
align %IAlign; #IMPLIED -- vertical or horizontal alignment --
hspace %Pixels; #IMPLIED -- horizontal gutter --
vspace %Pixels; #IMPLIED -- vertical gutter --
>
<!--=================== Horizontal Rule ==================================-->
<!ELEMENT HR - O EMPTY -- horizontal rule -->
<!ATTLIST HR
%attrs; -- %coreattrs, %i18n, %events --
align (left|center|right) #IMPLIED
noshade (noshade) #IMPLIED
size %Pixels; #IMPLIED
width %Length; #IMPLIED
>
<!--=================== Paragraphs =======================================-->
<!ELEMENT P - O (%inline;)* -- paragraph -->
<!ATTLIST P
%attrs; -- %coreattrs, %i18n, %events --
%align; -- align, text alignment --
>
<!--=================== Headings =========================================-->
<!--
There are six levels of headings from H1 (the most important)
to H6 (the least important).
-->
<!ELEMENT (%heading;) - - (%inline;)* -- heading -->
<!ATTLIST (%heading;)
%attrs; -- %coreattrs, %i18n, %events --
%align; -- align, text alignment --
>
<!--=================== Preformatted Text ================================-->
<!-- excludes markup for images and changes in font size -->
<!ENTITY % pre.exclusion "IMG|OBJECT|APPLET|BIG|SMALL|SUB|SUP|FONT|BASEFONT">
<!ELEMENT PRE - - (%inline;)* -(%pre.exclusion;) -- preformatted text -->
<!ATTLIST PRE
%attrs; -- %coreattrs, %i18n, %events --
width NUMBER #IMPLIED
>
<!--===================== Inline Quotes ==================================-->
<!ELEMENT Q - - (%inline;)* -- short inline quotation -->
<!ATTLIST Q
%attrs; -- %coreattrs, %i18n, %events --
cite %URI; #IMPLIED -- URI for source document or msg --
>
<!--=================== Block-like Quotes ================================-->
<!ELEMENT BLOCKQUOTE - - (%flow;)* -- long quotation -->
<!ATTLIST BLOCKQUOTE
%attrs; -- %coreattrs, %i18n, %events --
cite %URI; #IMPLIED -- URI for source document or msg --
>
<!--=================== Inserted/Deleted Text ============================-->
<!-- INS/DEL are handled by inclusion on BODY -->
<!ELEMENT (INS|DEL) - - (%flow;)* -- inserted text, deleted text -->
<!ATTLIST (INS|DEL)
%attrs; -- %coreattrs, %i18n, %events --
cite %URI; #IMPLIED -- info on reason for change --
datetime %Datetime; #IMPLIED -- date and time of change --
>
<!--=================== Lists ============================================-->
<!-- definition lists - DT for term, DD for its definition -->
<!ELEMENT DL - - (DT|DD)+ -- definition list -->
<!ATTLIST DL
%attrs; -- %coreattrs, %i18n, %events --
compact (compact) #IMPLIED -- reduced interitem spacing --
>
<!ELEMENT DT - O (%inline;)* -- definition term -->
<!ELEMENT DD - O (%flow;)* -- definition description -->
<!ATTLIST (DT|DD)
%attrs; -- %coreattrs, %i18n, %events --
>
<!-- Ordered lists (OL) Numbering style
1 arablic numbers 1, 2, 3, ...
a lower alpha a, b, c, ...
A upper alpha A, B, C, ...
i lower roman i, ii, iii, ...
I upper roman I, II, III, ...
The style is applied to the sequence number which by default
is reset to 1 for the first list item in an ordered list.
This can't be expressed directly in SGML due to case folding.
-->
<!ENTITY % OLStyle "CDATA" -- constrained to: "(1|a|A|i|I)" -->
<!ELEMENT OL - - (LI)+ -- ordered list -->
<!ATTLIST OL
%attrs; -- %coreattrs, %i18n, %events --
type %OLStyle; #IMPLIED -- numbering style --
compact (compact) #IMPLIED -- reduced interitem spacing --
start NUMBER #IMPLIED -- starting sequence number --
>
<!-- Unordered Lists (UL) bullet styles -->
<!ENTITY % ULStyle "(disc|square|circle)">
<!ELEMENT UL - - (LI)+ -- unordered list -->
<!ATTLIST UL
%attrs; -- %coreattrs, %i18n, %events --
type %ULStyle; #IMPLIED -- bullet style --
compact (compact) #IMPLIED -- reduced interitem spacing --
>
<!ELEMENT (DIR|MENU) - - (LI)+ -(%block;) -- directory list, menu list -->
<!ATTLIST DIR
%attrs; -- %coreattrs, %i18n, %events --
compact (compact) #IMPLIED -- reduced interitem spacing --
>
<!ATTLIST MENU
%attrs; -- %coreattrs, %i18n, %events --
compact (compact) #IMPLIED -- reduced interitem spacing --
>
<!ENTITY % LIStyle "CDATA" -- constrained to: "(%ULStyle;|%OLStyle;)" -->
<!ELEMENT LI - O (%flow;)* -- list item -->
<!ATTLIST LI
%attrs; -- %coreattrs, %i18n, %events --
type %LIStyle; #IMPLIED -- list item style --
value NUMBER #IMPLIED -- reset sequence number --
>
<!--================ Forms ===============================================-->
<!ELEMENT FORM - - (%flow;)* -(FORM) -- interactive form -->
<!ATTLIST FORM
%attrs; -- %coreattrs, %i18n, %events --
action %URI; #REQUIRED -- server-side form handler --
method (GET|POST) GET -- HTTP method used to submit the form--
enctype %ContentType; "application/x-www-form-urlencoded"
accept %ContentTypes; #IMPLIED -- list of MIME types for file upload --
name CDATA #IMPLIED -- name of form for scripting --
onsubmit %Script; #IMPLIED -- the form was submitted --
onreset %Script; #IMPLIED -- the form was reset --
target %FrameTarget; #IMPLIED -- render in this frame --
accept-charset %Charsets; #IMPLIED -- list of supported charsets --
>
<!-- Each label must not contain more than ONE field -->
<!ELEMENT LABEL - - (%inline;)* -(LABEL) -- form field label text -->
<!ATTLIST LABEL
%attrs; -- %coreattrs, %i18n, %events --
for IDREF #IMPLIED -- matches field ID value --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
>
<!ENTITY % InputType
"(TEXT | PASSWORD | CHECKBOX |
RADIO | SUBMIT | RESET |
FILE | HIDDEN | IMAGE | BUTTON)"
>
<!-- attribute name required for all but submit and reset -->
<!ELEMENT INPUT - O EMPTY -- form control -->
<!ATTLIST INPUT
%attrs; -- %coreattrs, %i18n, %events --
type %InputType; TEXT -- what kind of widget is needed --
name CDATA #IMPLIED -- submit as part of form --
value CDATA #IMPLIED -- Specify for radio buttons and checkbo
xes --
checked (checked) #IMPLIED -- for radio buttons and check boxes --
disabled (disabled) #IMPLIED -- unavailable in this context --
readonly (readonly) #IMPLIED -- for text and passwd --
size CDATA #IMPLIED -- specific to each type of field --
maxlength NUMBER #IMPLIED -- max chars for text fields --
src %URI; #IMPLIED -- for fields with images --
alt CDATA #IMPLIED -- short description --
usemap %URI; #IMPLIED -- use client-side image map --
ismap (ismap) #IMPLIED -- use server-side image map --
tabindex NUMBER #IMPLIED -- position in tabbing order --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
onselect %Script; #IMPLIED -- some text was selected --
onchange %Script; #IMPLIED -- the element value was changed --
accept %ContentTypes; #IMPLIED -- list of MIME types for file upload --
align %IAlign; #IMPLIED -- vertical or horizontal alignment --
%reserved; -- reserved for possible future use --
>
<!ELEMENT SELECT - - (OPTGROUP|OPTION)+ -- option selector -->
<!ATTLIST SELECT
%attrs; -- %coreattrs, %i18n, %events --
name CDATA #IMPLIED -- field name --
size NUMBER #IMPLIED -- rows visible --
multiple (multiple) #IMPLIED -- default is single selection --
disabled (disabled) #IMPLIED -- unavailable in this context --
tabindex NUMBER #IMPLIED -- position in tabbing order --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
onchange %Script; #IMPLIED -- the element value was changed --
%reserved; -- reserved for possible future use --
>
<!ELEMENT OPTGROUP - - (OPTION)+ -- option group -->
<!ATTLIST OPTGROUP
%attrs; -- %coreattrs, %i18n, %events --
disabled (disabled) #IMPLIED -- unavailable in this context --
label %Text; #REQUIRED -- for use in hierarchical menus --
>
<!ELEMENT OPTION - O (#PCDATA) -- selectable choice -->
<!ATTLIST OPTION
%attrs; -- %coreattrs, %i18n, %events --
selected (selected) #IMPLIED
disabled (disabled) #IMPLIED -- unavailable in this context --
label %Text; #IMPLIED -- for use in hierarchical menus --
value CDATA #IMPLIED -- defaults to element content --
>
<!ELEMENT TEXTAREA - - (#PCDATA) -- multi-line text field -->
<!ATTLIST TEXTAREA
%attrs; -- %coreattrs, %i18n, %events --
name CDATA #IMPLIED
rows NUMBER #REQUIRED
cols NUMBER #REQUIRED
disabled (disabled) #IMPLIED -- unavailable in this context --
readonly (readonly) #IMPLIED
tabindex NUMBER #IMPLIED -- position in tabbing order --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
onselect %Script; #IMPLIED -- some text was selected --
onchange %Script; #IMPLIED -- the element value was changed --
%reserved; -- reserved for possible future use --
>
<!--
#PCDATA is to solve the mixed content problem,
per specification only whitespace is allowed there!
-->
<!ELEMENT FIELDSET - - (#PCDATA,LEGEND,(%flow;)*) -- form control group -->
<!ATTLIST FIELDSET
%attrs; -- %coreattrs, %i18n, %events --
>
<!ELEMENT LEGEND - - (%inline;)* -- fieldset legend -->
<!ENTITY % LAlign "(top|bottom|left|right)">
<!ATTLIST LEGEND
%attrs; -- %coreattrs, %i18n, %events --
accesskey %Character; #IMPLIED -- accessibility key character --
align %LAlign; #IMPLIED -- relative to fieldset --
>
<!ELEMENT BUTTON - -
(%flow;)* -(A|%formctrl;|FORM|ISINDEX|FIELDSET|IFRAME)
-- push button -->
<!ATTLIST BUTTON
%attrs; -- %coreattrs, %i18n, %events --
name CDATA #IMPLIED
value CDATA #IMPLIED -- sent to server when submitted --
type (button|submit|reset) submit -- for use as form button --
disabled (disabled) #IMPLIED -- unavailable in this context --
tabindex NUMBER #IMPLIED -- position in tabbing order --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
%reserved; -- reserved for possible future use --
>
<!--======================= Tables =======================================-->
<!-- IETF HTML table standard, see [RFC1942] -->
<!--
The BORDER attribute sets the thickness of the frame around the
table. The default units are screen pixels.
The FRAME attribute specifies which parts of the frame around
the table should be rendered. The values are not the same as
CALS to avoid a name clash with the VALIGN attribute.
The value "border" is included for backwards compatibility with
<TABLE BORDER> which yields frame=border and border=implied
For <TABLE BORDER=1> you get border=1 and frame=implied. In this
case, it is appropriate to treat this as frame=border for backwards
compatibility with deployed browsers.
-->
<!ENTITY % TFrame "(void|above|below|hsides|lhs|rhs|vsides|box|border)">
<!--
The RULES attribute defines which rules to draw between cells:
If RULES is absent then assume:
"none" if BORDER is absent or BORDER=0 otherwise "all"
-->
<!ENTITY % TRules "(none | groups | rows | cols | all)">
<!-- horizontal placement of table relative to document -->
<!ENTITY % TAlign "(left|center|right)">
<!-- horizontal alignment attributes for cell contents -->
<!ENTITY % cellhalign
"align (left|center|right|justify|char) #IMPLIED
char %Character; #IMPLIED -- alignment char, e.g. char=':' --
charoff %Length; #IMPLIED -- offset for alignment char --"
>
<!-- vertical alignment attributes for cell contents -->
<!ENTITY % cellvalign
"valign (top|middle|bottom|baseline) #IMPLIED"
>
<!ELEMENT TABLE - -
(CAPTION?, (COL*|COLGROUP*), THEAD?, TFOOT?, TBODY+)>
<!ELEMENT CAPTION - - (%inline;)* -- table caption -->
<!ELEMENT THEAD - O (TR)+ -- table header -->
<!ELEMENT TFOOT - O (TR)+ -- table footer -->
<!ELEMENT TBODY O O (TR)+ -- table body -->
<!ELEMENT COLGROUP - O (COL)* -- table column group -->
<!ELEMENT COL - O EMPTY -- table column -->
<!ELEMENT TR - O (TH|TD)+ -- table row -->
<!ELEMENT (TH|TD) - O (%flow;)* -- table header cell, table data cell-->
<!ATTLIST TABLE -- table element --
%attrs; -- %coreattrs, %i18n, %events --
summary %Text; #IMPLIED -- purpose/structure for speech output--
width %Length; #IMPLIED -- table width --
border %Pixels; #IMPLIED -- controls frame width around table --
frame %TFrame; #IMPLIED -- which parts of frame to render --
rules %TRules; #IMPLIED -- rulings between rows and cols --
cellspacing %Length; #IMPLIED -- spacing between cells --
cellpadding %Length; #IMPLIED -- spacing within cells --
align %TAlign; #IMPLIED -- table position relative to window --
bgcolor %Color; #IMPLIED -- background color for cells --
%reserved; -- reserved for possible future use --
datapagesize CDATA #IMPLIED -- reserved for possible future use --
>
<!ENTITY % CAlign "(top|bottom|left|right)">
<!ATTLIST CAPTION
%attrs; -- %coreattrs, %i18n, %events --
align %CAlign; #IMPLIED -- relative to table --
>
<!--
COLGROUP groups a set of COL elements. It allows you to group
several semantically related columns together.
-->
<!ATTLIST COLGROUP
%attrs; -- %coreattrs, %i18n, %events --
span NUMBER 1 -- default number of columns in group --
width %MultiLength; #IMPLIED -- default width for enclosed COLs --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
>
<!--
COL elements define the alignment properties for cells in
one or more columns.
The WIDTH attribute specifies the width of the columns, e.g.
width=64 width in screen pixels
width=0.5* relative width of 0.5
The SPAN attribute causes the attributes of one
COL element to apply to more than one column.
-->
<!ATTLIST COL -- column groups and properties --
%attrs; -- %coreattrs, %i18n, %events --
span NUMBER 1 -- COL attributes affect N columns --
width %MultiLength; #IMPLIED -- column width specification --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
>
<!--
Use THEAD to duplicate headers when breaking table
across page boundaries, or for static headers when
TBODY sections are rendered in scrolling panel.
Use TFOOT to duplicate footers when breaking table
across page boundaries, or for static footers when
TBODY sections are rendered in scrolling panel.
Use multiple TBODY sections when rules are needed
between groups of table rows.
-->
<!ATTLIST (THEAD|TBODY|TFOOT) -- table section --
%attrs; -- %coreattrs, %i18n, %events --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
>
<!ATTLIST TR -- table row --
%attrs; -- %coreattrs, %i18n, %events --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
bgcolor %Color; #IMPLIED -- background color for row --
>
<!-- Scope is simpler than headers attribute for common tables -->
<!ENTITY % Scope "(row|col|rowgroup|colgroup)">
<!-- TH is for headers, TD for data, but for cells acting as both use TD -->
<!ATTLIST (TH|TD) -- header or data cell --
%attrs; -- %coreattrs, %i18n, %events --
abbr %Text; #IMPLIED -- abbreviation for header cell --
axis CDATA #IMPLIED -- comma-separated list of related heade
rs--
headers IDREFS #IMPLIED -- list of id's for header cells --
scope %Scope; #IMPLIED -- scope covered by header cells --
rowspan NUMBER 1 -- number of rows spanned by cell --
colspan NUMBER 1 -- number of cols spanned by cell --
%cellhalign; -- horizontal alignment in cells --
%cellvalign; -- vertical alignment in cells --
nowrap (nowrap) #IMPLIED -- suppress word wrap --
bgcolor %Color; #IMPLIED -- cell background color --
width %Length; #IMPLIED -- width for cell --
height %Length; #IMPLIED -- height for cell --
>
<!--================== Document Frames ===================================-->
<!--
The content model for HTML documents depends on whether the HEAD is
followed by a FRAMESET or BODY element. The widespread omission of
the BODY start tag makes it impractical to define the content model
without the use of a marked section.
-->
<![ %HTML.Frameset; [
<!ELEMENT FRAMESET - - ((FRAMESET|FRAME)+ & NOFRAMES?) -- window subdivision-->
<!ATTLIST FRAMESET
%coreattrs; -- id, class, style, title --
rows %MultiLengths; #IMPLIED -- list of lengths,
default: 100% (1 row) --
cols %MultiLengths; #IMPLIED -- list of lengths,
default: 100% (1 col) --
onload %Script; #IMPLIED -- all the frames have been loaded --
onunload %Script; #IMPLIED -- all the frames have been removed --
>
]]>
<![ %HTML.Frameset; [
<!-- reserved frame names start with "_" otherwise starts with letter -->
<!ELEMENT FRAME - O EMPTY -- subwindow -->
<!ATTLIST FRAME
%coreattrs; -- id, class, style, title --
longdesc %URI; #IMPLIED -- link to long description
(complements title) --
name CDATA #IMPLIED -- name of frame for targetting --
src %URI; #IMPLIED -- source of frame content --
frameborder (1|0) 1 -- request frame borders? --
marginwidth %Pixels; #IMPLIED -- margin widths in pixels --
marginheight %Pixels; #IMPLIED -- margin height in pixels --
noresize (noresize) #IMPLIED -- allow users to resize frames? --
scrolling (yes|no|auto) auto -- scrollbar or none --
>
]]>
<!ELEMENT IFRAME - - (%flow;)* -- inline subwindow -->
<!ATTLIST IFRAME
%coreattrs; -- id, class, style, title --
longdesc %URI; #IMPLIED -- link to long description
(complements title) --
name CDATA #IMPLIED -- name of frame for targetting --
src %URI; #IMPLIED -- source of frame content --
frameborder (1|0) 1 -- request frame borders? --
marginwidth %Pixels; #IMPLIED -- margin widths in pixels --
marginheight %Pixels; #IMPLIED -- margin height in pixels --
scrolling (yes|no|auto) auto -- scrollbar or none --
align %IAlign; #IMPLIED -- vertical or horizontal alignment --
height %Length; #IMPLIED -- frame height --
width %Length; #IMPLIED -- frame width --
>
<![ %HTML.Frameset; [
<!ENTITY % noframes.content "(BODY) -(NOFRAMES)">
]]>
<!ENTITY % noframes.content "(%flow;)*">
<!ELEMENT NOFRAMES - - %noframes.content;
-- alternate content container for non frame-based rendering -->
<!ATTLIST NOFRAMES
%attrs; -- %coreattrs, %i18n, %events --
>
<!--================ Document Head =======================================-->
<!-- %head.misc; defined earlier on as "SCRIPT|STYLE|META|LINK|OBJECT" -->
<!ENTITY % head.content "TITLE & ISINDEX? & BASE?">
<!ELEMENT HEAD O O (%head.content;) +(%head.misc;) -- document head -->
<!ATTLIST HEAD
%i18n; -- lang, dir --
profile %URI; #IMPLIED -- named dictionary of meta info --
>
<!-- The TITLE element is not considered part of the flow of text.
It should be displayed, for example as the page header or
window title. Exactly one title is required per document.
-->
<!ELEMENT TITLE - - (#PCDATA) -(%head.misc;) -- document title -->
<!ATTLIST TITLE %i18n>
<!ELEMENT ISINDEX - O EMPTY -- single line prompt -->
<!ATTLIST ISINDEX
%coreattrs; -- id, class, style, title --
%i18n; -- lang, dir --
prompt %Text; #IMPLIED -- prompt message -->
<!ELEMENT BASE - O EMPTY -- document base URI -->
<!ATTLIST BASE
href %URI; #IMPLIED -- URI that acts as base URI --
target %FrameTarget; #IMPLIED -- render in this frame --
>
<!ELEMENT META - O EMPTY -- generic metainformation -->
<!ATTLIST META
%i18n; -- lang, dir, for use with content --
http-equiv NAME #IMPLIED -- HTTP response header name --
name NAME #IMPLIED -- metainformation name --
content CDATA #REQUIRED -- associated information --
scheme CDATA #IMPLIED -- select form of content --
>
<!ELEMENT STYLE - - %StyleSheet -- style info -->
<!ATTLIST STYLE
%i18n; -- lang, dir, for use with title --
type %ContentType; #REQUIRED -- content type of style language --
media %MediaDesc; #IMPLIED -- designed for use with these media --
title %Text; #IMPLIED -- advisory title --
>
<!ELEMENT SCRIPT - - %Script; -- script statements -->
<!ATTLIST SCRIPT
charset %Charset; #IMPLIED -- char encoding of linked resource --
type %ContentType; #REQUIRED -- content type of script language --
language CDATA #IMPLIED -- predefined script language name --
src %URI; #IMPLIED -- URI for an external script --
defer (defer) #IMPLIED -- UA may defer execution of script --
event CDATA #IMPLIED -- reserved for possible future use --
for %URI; #IMPLIED -- reserved for possible future use --
>
<!ELEMENT NOSCRIPT - - (%flow;)*
-- alternate content container for non script-based rendering -->
<!ATTLIST NOSCRIPT
%attrs; -- %coreattrs, %i18n, %events --
>
<!--================ Document Structure ==================================-->
<!ENTITY % version "version CDATA #FIXED '%HTML.Version;'">
<![ %HTML.Frameset; [
<!ENTITY % html.content "HEAD, FRAMESET">
]]>
<!ENTITY % html.content "HEAD, BODY">
<!ELEMENT HTML O O (%html.content;) -- document root element -->
<!ATTLIST HTML
%i18n; -- lang, dir --
%version;
>
23 Frameset Document Type Definition
<!--
This is the HTML 4.01 Frameset DTD, which should be
used for documents with frames. This DTD is identical
to the HTML 4.01 Transitional DTD except for the
content model of the "HTML" element: in frameset
documents, the "FRAMESET" element replaces the "BODY"
element.
Draft: $Date: 1999/12/24 23:37:46 $
Authors:
Dave Raggett <dsr@w3.org>
Arnaud Le Hors <lehors@w3.org>
Ian Jacobs <ij@w3.org>
Further information about HTML 4.01 is available at:
http://www.w3.org/TR/1999/REC-html401-19991224.
-->
<!ENTITY % HTML.Version "-//W3C//DTD HTML 4.01 Frameset//EN"
-- Typical usage:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<html>
<head>
...
</head>
<frameset>
...
</frameset>
</html>
-->
<!ENTITY % HTML.Frameset "INCLUDE">
<!ENTITY % HTML4.dtd PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
%HTML4.dtd;
24 Character entity references in HTML 4
Contents
1. Introduction to character entity references
2. Character entity references for ISO 8859-1 characters
1. The list of characters
3. Character entity references for symbols, mathematical symbols, and
Greek letters
1. The list of characters
4. Character entity references for markup-significant and
internationalization characters
1. The list of characters
24.1 Introduction to character entity references
A character entity reference is an SGML construct that references a
character of the document character set.
This version of HTML supports several sets of character entity
references:
* ISO 8859-1 (Latin-1) characters In accordance with section 14 of
[RFC1866], the set of Latin-1 entities has been extended by this
specification to cover the whole right part of ISO-8859-1 (all
code positions with the high-order bit set), including the already
commonly used , © and ®. The names of the entities
are taken from the appendices of SGML (defined in [ISO8879]).
* symbols, mathematical symbols, and Greek letters. These characters
may be represented by glyphs in the Adobe font "Symbol".
* markup-significant and internationalization characters (e.g., for
bidirectional text).
The following sections present the complete lists of character entity
references. Although, by convention, [ISO10646] the comments following
each entry are usually written with uppercase letters, we have
converted them to lowercase in this specification for reasons of
readability.
24.2 Character entity references for ISO 8859-1 characters
The character entity references in this section produce characters
whose numeric equivalents should already be supported by conforming
HTML 2.0 user agents. Thus, the character entity reference ÷ is
a more convenient form than ÷ for obtaining the division sign
(÷).
To support these named entities, user agents need only recognize the
entity names and convert them to characters that lie within the
repertoire of [ISO88591].
Character 65533 (FFFD hexadecimal) is the last valid character in
UCS-2. 65534 (FFFE hexadecimal) is unassigned and reserved as the
byte-swapped version of ZERO WIDTH NON-BREAKING SPACE for byte-order
detection purposes. 65535 (FFFF hexadecimal) is unassigned.
24.2.1 The list of characters
<!-- Portions © International Organization for Standardization 1986
Permission to copy in any form is granted for use with
conforming SGML systems and applications as defined in
ISO 8879, provided this notice is included in all copies.
-->
<!-- Character entity set. Typical invocation:
<!ENTITY % HTMLlat1 PUBLIC
"-//W3C//ENTITIES Latin 1//EN//HTML">
%HTMLlat1;
-->
<!ENTITY nbsp CDATA " " -- no-break space = non-breaking space,
U+00A0 ISOnum -->
<!ENTITY iexcl CDATA "¡" -- inverted exclamation mark, U+00A1 ISOnum -->
<!ENTITY cent CDATA "¢" -- cent sign, U+00A2 ISOnum -->
<!ENTITY pound CDATA "£" -- pound sign, U+00A3 ISOnum -->
<!ENTITY curren CDATA "¤" -- currency sign, U+00A4 ISOnum -->
<!ENTITY yen CDATA "¥" -- yen sign = yuan sign, U+00A5 ISOnum -->
<!ENTITY brvbar CDATA "¦" -- broken bar = broken vertical bar,
U+00A6 ISOnum -->
<!ENTITY sect CDATA "§" -- section sign, U+00A7 ISOnum -->
<!ENTITY uml CDATA "¨" -- diaeresis = spacing diaeresis,
U+00A8 ISOdia -->
<!ENTITY copy CDATA "©" -- copyright sign, U+00A9 ISOnum -->
<!ENTITY ordf CDATA "ª" -- feminine ordinal indicator, U+00AA ISOnum -->
<!ENTITY laquo CDATA "«" -- left-pointing double angle quotation mark
= left pointing guillemet, U+00AB ISOnum -->
<!ENTITY not CDATA "¬" -- not sign, U+00AC ISOnum -->
<!ENTITY shy CDATA "­" -- soft hyphen = discretionary hyphen,
U+00AD ISOnum -->
<!ENTITY reg CDATA "®" -- registered sign = registered trade mark sign,
U+00AE ISOnum -->
<!ENTITY macr CDATA "¯" -- macron = spacing macron = overline
= APL overbar, U+00AF ISOdia -->
<!ENTITY deg CDATA "°" -- degree sign, U+00B0 ISOnum -->
<!ENTITY plusmn CDATA "±" -- plus-minus sign = plus-or-minus sign,
U+00B1 ISOnum -->
<!ENTITY sup2 CDATA "²" -- superscript two = superscript digit two
= squared, U+00B2 ISOnum -->
<!ENTITY sup3 CDATA "³" -- superscript three = superscript digit three
= cubed, U+00B3 ISOnum -->
<!ENTITY acute CDATA "´" -- acute accent = spacing acute,
U+00B4 ISOdia -->
<!ENTITY micro CDATA "µ" -- micro sign, U+00B5 ISOnum -->
<!ENTITY para CDATA "¶" -- pilcrow sign = paragraph sign,
U+00B6 ISOnum -->
<!ENTITY middot CDATA "·" -- middle dot = Georgian comma
= Greek middle dot, U+00B7 ISOnum -->
<!ENTITY cedil CDATA "¸" -- cedilla = spacing cedilla, U+00B8 ISOdia -->
<!ENTITY sup1 CDATA "¹" -- superscript one = superscript digit one,
U+00B9 ISOnum -->
<!ENTITY ordm CDATA "º" -- masculine ordinal indicator,
U+00BA ISOnum -->
<!ENTITY raquo CDATA "»" -- right-pointing double angle quotation mark
= right pointing guillemet, U+00BB ISOnum -->
<!ENTITY frac14 CDATA "¼" -- vulgar fraction one quarter
= fraction one quarter, U+00BC ISOnum -->
<!ENTITY frac12 CDATA "½" -- vulgar fraction one half
= fraction one half, U+00BD ISOnum -->
<!ENTITY frac34 CDATA "¾" -- vulgar fraction three quarters
= fraction three quarters, U+00BE ISOnum -->
<!ENTITY iquest CDATA "¿" -- inverted question mark
= turned question mark, U+00BF ISOnum -->
<!ENTITY Agrave CDATA "À" -- latin capital letter A with grave
= latin capital letter A grave,
U+00C0 ISOlat1 -->
<!ENTITY Aacute CDATA "Á" -- latin capital letter A with acute,
U+00C1 ISOlat1 -->
<!ENTITY Acirc CDATA "Â" -- latin capital letter A with circumflex,
U+00C2 ISOlat1 -->
<!ENTITY Atilde CDATA "Ã" -- latin capital letter A with tilde,
U+00C3 ISOlat1 -->
<!ENTITY Auml CDATA "Ä" -- latin capital letter A with diaeresis,
U+00C4 ISOlat1 -->
<!ENTITY Aring CDATA "Å" -- latin capital letter A with ring above
= latin capital letter A ring,
U+00C5 ISOlat1 -->
<!ENTITY AElig CDATA "Æ" -- latin capital letter AE
= latin capital ligature AE,
U+00C6 ISOlat1 -->
<!ENTITY Ccedil CDATA "Ç" -- latin capital letter C with cedilla,
U+00C7 ISOlat1 -->
<!ENTITY Egrave CDATA "È" -- latin capital letter E with grave,
U+00C8 ISOlat1 -->
<!ENTITY Eacute CDATA "É" -- latin capital letter E with acute,
U+00C9 ISOlat1 -->
<!ENTITY Ecirc CDATA "Ê" -- latin capital letter E with circumflex,
U+00CA ISOlat1 -->
<!ENTITY Euml CDATA "Ë" -- latin capital letter E with diaeresis,
U+00CB ISOlat1 -->
<!ENTITY Igrave CDATA "Ì" -- latin capital letter I with grave,
U+00CC ISOlat1 -->
<!ENTITY Iacute CDATA "Í" -- latin capital letter I with acute,
U+00CD ISOlat1 -->
<!ENTITY Icirc CDATA "Î" -- latin capital letter I with circumflex,
U+00CE ISOlat1 -->
<!ENTITY Iuml CDATA "Ï" -- latin capital letter I with diaeresis,
U+00CF ISOlat1 -->
<!ENTITY ETH CDATA "Ð" -- latin capital letter ETH, U+00D0 ISOlat1 -->
<!ENTITY Ntilde CDATA "Ñ" -- latin capital letter N with tilde,
U+00D1 ISOlat1 -->
<!ENTITY Ograve CDATA "Ò" -- latin capital letter O with grave,
U+00D2 ISOlat1 -->
<!ENTITY Oacute CDATA "Ó" -- latin capital letter O with acute,
U+00D3 ISOlat1 -->
<!ENTITY Ocirc CDATA "Ô" -- latin capital letter O with circumflex,
U+00D4 ISOlat1 -->
<!ENTITY Otilde CDATA "Õ" -- latin capital letter O with tilde,
U+00D5 ISOlat1 -->
<!ENTITY Ouml CDATA "Ö" -- latin capital letter O with diaeresis,
U+00D6 ISOlat1 -->
<!ENTITY times CDATA "×" -- multiplication sign, U+00D7 ISOnum -->
<!ENTITY Oslash CDATA "Ø" -- latin capital letter O with stroke
= latin capital letter O slash,
U+00D8 ISOlat1 -->
<!ENTITY Ugrave CDATA "Ù" -- latin capital letter U with grave,
U+00D9 ISOlat1 -->
<!ENTITY Uacute CDATA "Ú" -- latin capital letter U with acute,
U+00DA ISOlat1 -->
<!ENTITY Ucirc CDATA "Û" -- latin capital letter U with circumflex,
U+00DB ISOlat1 -->
<!ENTITY Uuml CDATA "Ü" -- latin capital letter U with diaeresis,
U+00DC ISOlat1 -->
<!ENTITY Yacute CDATA "Ý" -- latin capital letter Y with acute,
U+00DD ISOlat1 -->
<!ENTITY THORN CDATA "Þ" -- latin capital letter THORN,
U+00DE ISOlat1 -->
<!ENTITY szlig CDATA "ß" -- latin small letter sharp s = ess-zed,
U+00DF ISOlat1 -->
<!ENTITY agrave CDATA "à" -- latin small letter a with grave
= latin small letter a grave,
U+00E0 ISOlat1 -->
<!ENTITY aacute CDATA "á" -- latin small letter a with acute,
U+00E1 ISOlat1 -->
<!ENTITY acirc CDATA "â" -- latin small letter a with circumflex,
U+00E2 ISOlat1 -->
<!ENTITY atilde CDATA "ã" -- latin small letter a with tilde,
U+00E3 ISOlat1 -->
<!ENTITY auml CDATA "ä" -- latin small letter a with diaeresis,
U+00E4 ISOlat1 -->
<!ENTITY aring CDATA "å" -- latin small letter a with ring above
= latin small letter a ring,
U+00E5 ISOlat1 -->
<!ENTITY aelig CDATA "æ" -- latin small letter ae
= latin small ligature ae, U+00E6 ISOlat1 -->
<!ENTITY ccedil CDATA "ç" -- latin small letter c with cedilla,
U+00E7 ISOlat1 -->
<!ENTITY egrave CDATA "è" -- latin small letter e with grave,
U+00E8 ISOlat1 -->
<!ENTITY eacute CDATA "é" -- latin small letter e with acute,
U+00E9 ISOlat1 -->
<!ENTITY ecirc CDATA "ê" -- latin small letter e with circumflex,
U+00EA ISOlat1 -->
<!ENTITY euml CDATA "ë" -- latin small letter e with diaeresis,
U+00EB ISOlat1 -->
<!ENTITY igrave CDATA "ì" -- latin small letter i with grave,
U+00EC ISOlat1 -->
<!ENTITY iacute CDATA "í" -- latin small letter i with acute,
U+00ED ISOlat1 -->
<!ENTITY icirc CDATA "î" -- latin small letter i with circumflex,
U+00EE ISOlat1 -->
<!ENTITY iuml CDATA "ï" -- latin small letter i with diaeresis,
U+00EF ISOlat1 -->
<!ENTITY eth CDATA "ð" -- latin small letter eth, U+00F0 ISOlat1 -->
<!ENTITY ntilde CDATA "ñ" -- latin small letter n with tilde,
U+00F1 ISOlat1 -->
<!ENTITY ograve CDATA "ò" -- latin small letter o with grave,
U+00F2 ISOlat1 -->
<!ENTITY oacute CDATA "ó" -- latin small letter o with acute,
U+00F3 ISOlat1 -->
<!ENTITY ocirc CDATA "ô" -- latin small letter o with circumflex,
U+00F4 ISOlat1 -->
<!ENTITY otilde CDATA "õ" -- latin small letter o with tilde,
U+00F5 ISOlat1 -->
<!ENTITY ouml CDATA "ö" -- latin small letter o with diaeresis,
U+00F6 ISOlat1 -->
<!ENTITY divide CDATA "÷" -- division sign, U+00F7 ISOnum -->
<!ENTITY oslash CDATA "ø" -- latin small letter o with stroke,
= latin small letter o slash,
U+00F8 ISOlat1 -->
<!ENTITY ugrave CDATA "ù" -- latin small letter u with grave,
U+00F9 ISOlat1 -->
<!ENTITY uacute CDATA "ú" -- latin small letter u with acute,
U+00FA ISOlat1 -->
<!ENTITY ucirc CDATA "û" -- latin small letter u with circumflex,
U+00FB ISOlat1 -->
<!ENTITY uuml CDATA "ü" -- latin small letter u with diaeresis,
U+00FC ISOlat1 -->
<!ENTITY yacute CDATA "ý" -- latin small letter y with acute,
U+00FD ISOlat1 -->
<!ENTITY thorn CDATA "þ" -- latin small letter thorn,
U+00FE ISOlat1 -->
<!ENTITY yuml CDATA "ÿ" -- latin small letter y with diaeresis,
U+00FF ISOlat1 -->
24.3 Character entity references for symbols, mathematical symbols, and Greek
letters
The character entity references in this section produce characters
that may be represented by glyphs in the widely available Adobe Symbol
font, including Greek characters, various bracketing symbols, and a
selection of mathematical operators such as gradient, product, and
summation symbols.
To support these entities, user agents may support full [ISO10646] or
use other means. Display of glyphs for these characters may be
obtained by being able to display the relevant [ISO10646] characters
or by other means, such as internally mapping the listed entities,
numeric character references, and characters to the appropriate
position in some font that contains the requisite glyphs.
When to use Greek entities. This entity set contains all the letters
used in modern Greek. However, it does not include Greek punctuation,
precomposed accented characters nor the non-spacing accents (tonos,
dialytika) required to compose them. There are no archaic letters,
Coptic-unique letters, or precomposed letters for Polytonic Greek. The
entities defined here are not intended for the representation of
modern Greek text and would not be an efficient representation;
rather, they are intended for occasional Greek letters used in
technical and mathematical works.
24.3.1 The list of characters
<!-- Mathematical, Greek and Symbolic characters for HTML -->
<!-- Character entity set. Typical invocation:
<!ENTITY % HTMLsymbol PUBLIC
"-//W3C//ENTITIES Symbols//EN//HTML">
%HTMLsymbol; -->
<!-- Portions © International Organization for Standardization 1986:
Permission to copy in any form is granted for use with
conforming SGML systems and applications as defined in
ISO 8879, provided this notice is included in all copies.
-->
<!-- Relevant ISO entity set is given unless names are newly introduced.
New names (i.e., not in ISO 8879 list) do not clash with any
existing ISO 8879 entity names. ISO 10646 character numbers
are given for each character, in hex. CDATA values are decimal
conversions of the ISO 10646 values and refer to the document
character set. Names are ISO 10646 names.
-->
<!-- Latin Extended-B -->
<!ENTITY fnof CDATA "ƒ" -- latin small f with hook = function
= florin, U+0192 ISOtech -->
<!-- Greek -->
<!ENTITY Alpha CDATA "Α" -- greek capital letter alpha, U+0391 -->
<!ENTITY Beta CDATA "Β" -- greek capital letter beta, U+0392 -->
<!ENTITY Gamma CDATA "Γ" -- greek capital letter gamma,
U+0393 ISOgrk3 -->
<!ENTITY Delta CDATA "Δ" -- greek capital letter delta,
U+0394 ISOgrk3 -->
<!ENTITY Epsilon CDATA "Ε" -- greek capital letter epsilon, U+0395 -->
<!ENTITY Zeta CDATA "Ζ" -- greek capital letter zeta, U+0396 -->
<!ENTITY Eta CDATA "Η" -- greek capital letter eta, U+0397 -->
<!ENTITY Theta CDATA "Θ" -- greek capital letter theta,
U+0398 ISOgrk3 -->
<!ENTITY Iota CDATA "Ι" -- greek capital letter iota, U+0399 -->
<!ENTITY Kappa CDATA "Κ" -- greek capital letter kappa, U+039A -->
<!ENTITY Lambda CDATA "Λ" -- greek capital letter lambda,
U+039B ISOgrk3 -->
<!ENTITY Mu CDATA "Μ" -- greek capital letter mu, U+039C -->
<!ENTITY Nu CDATA "Ν" -- greek capital letter nu, U+039D -->
<!ENTITY Xi CDATA "Ξ" -- greek capital letter xi, U+039E ISOgrk3 -->
<!ENTITY Omicron CDATA "Ο" -- greek capital letter omicron, U+039F -->
<!ENTITY Pi CDATA "Π" -- greek capital letter pi, U+03A0 ISOgrk3 -->
<!ENTITY Rho CDATA "Ρ" -- greek capital letter rho, U+03A1 -->
<!-- there is no Sigmaf, and no U+03A2 character either -->
<!ENTITY Sigma CDATA "Σ" -- greek capital letter sigma,
U+03A3 ISOgrk3 -->
<!ENTITY Tau CDATA "Τ" -- greek capital letter tau, U+03A4 -->
<!ENTITY Upsilon CDATA "Υ" -- greek capital letter upsilon,
U+03A5 ISOgrk3 -->
<!ENTITY Phi CDATA "Φ" -- greek capital letter phi,
U+03A6 ISOgrk3 -->
<!ENTITY Chi CDATA "Χ" -- greek capital letter chi, U+03A7 -->
<!ENTITY Psi CDATA "Ψ" -- greek capital letter psi,
U+03A8 ISOgrk3 -->
<!ENTITY Omega CDATA "Ω" -- greek capital letter omega,
U+03A9 ISOgrk3 -->
<!ENTITY alpha CDATA "α" -- greek small letter alpha,
U+03B1 ISOgrk3 -->
<!ENTITY beta CDATA "β" -- greek small letter beta, U+03B2 ISOgrk3 -->
<!ENTITY gamma CDATA "γ" -- greek small letter gamma,
U+03B3 ISOgrk3 -->
<!ENTITY delta CDATA "δ" -- greek small letter delta,
U+03B4 ISOgrk3 -->
<!ENTITY epsilon CDATA "ε" -- greek small letter epsilon,
U+03B5 ISOgrk3 -->
<!ENTITY zeta CDATA "ζ" -- greek small letter zeta, U+03B6 ISOgrk3 -->
<!ENTITY eta CDATA "η" -- greek small letter eta, U+03B7 ISOgrk3 -->
<!ENTITY theta CDATA "θ" -- greek small letter theta,
U+03B8 ISOgrk3 -->
<!ENTITY iota CDATA "ι" -- greek small letter iota, U+03B9 ISOgrk3 -->
<!ENTITY kappa CDATA "κ" -- greek small letter kappa,
U+03BA ISOgrk3 -->
<!ENTITY lambda CDATA "λ" -- greek small letter lambda,
U+03BB ISOgrk3 -->
<!ENTITY mu CDATA "μ" -- greek small letter mu, U+03BC ISOgrk3 -->
<!ENTITY nu CDATA "ν" -- greek small letter nu, U+03BD ISOgrk3 -->
<!ENTITY xi CDATA "ξ" -- greek small letter xi, U+03BE ISOgrk3 -->
<!ENTITY omicron CDATA "ο" -- greek small letter omicron, U+03BF NEW -->
<!ENTITY pi CDATA "π" -- greek small letter pi, U+03C0 ISOgrk3 -->
<!ENTITY rho CDATA "ρ" -- greek small letter rho, U+03C1 ISOgrk3 -->
<!ENTITY sigmaf CDATA "ς" -- greek small letter final sigma,
U+03C2 ISOgrk3 -->
<!ENTITY sigma CDATA "σ" -- greek small letter sigma,
U+03C3 ISOgrk3 -->
<!ENTITY tau CDATA "τ" -- greek small letter tau, U+03C4 ISOgrk3 -->
<!ENTITY upsilon CDATA "υ" -- greek small letter upsilon,
U+03C5 ISOgrk3 -->
<!ENTITY phi CDATA "φ" -- greek small letter phi, U+03C6 ISOgrk3 -->
<!ENTITY chi CDATA "χ" -- greek small letter chi, U+03C7 ISOgrk3 -->
<!ENTITY psi CDATA "ψ" -- greek small letter psi, U+03C8 ISOgrk3 -->
<!ENTITY omega CDATA "ω" -- greek small letter omega,
U+03C9 ISOgrk3 -->
<!ENTITY thetasym CDATA "ϑ" -- greek small letter theta symbol,
U+03D1 NEW -->
<!ENTITY upsih CDATA "ϒ" -- greek upsilon with hook symbol,
U+03D2 NEW -->
<!ENTITY piv CDATA "ϖ" -- greek pi symbol, U+03D6 ISOgrk3 -->
<!-- General Punctuation -->
<!ENTITY bull CDATA "•" -- bullet = black small circle,
U+2022 ISOpub -->
<!-- bullet is NOT the same as bullet operator, U+2219 -->
<!ENTITY hellip CDATA "…" -- horizontal ellipsis = three dot leader,
U+2026 ISOpub -->
<!ENTITY prime CDATA "′" -- prime = minutes = feet, U+2032 ISOtech -->
<!ENTITY Prime CDATA "″" -- double prime = seconds = inches,
U+2033 ISOtech -->
<!ENTITY oline CDATA "‾" -- overline = spacing overscore,
U+203E NEW -->
<!ENTITY frasl CDATA "⁄" -- fraction slash, U+2044 NEW -->
<!-- Letterlike Symbols -->
<!ENTITY weierp CDATA "℘" -- script capital P = power set
= Weierstrass p, U+2118 ISOamso -->
<!ENTITY image CDATA "ℑ" -- blackletter capital I = imaginary part,
U+2111 ISOamso -->
<!ENTITY real CDATA "ℜ" -- blackletter capital R = real part symbol,
U+211C ISOamso -->
<!ENTITY trade CDATA "™" -- trade mark sign, U+2122 ISOnum -->
<!ENTITY alefsym CDATA "ℵ" -- alef symbol = first transfinite cardinal,
U+2135 NEW -->
<!-- alef symbol is NOT the same as hebrew letter alef,
U+05D0 although the same glyph could be used to depict both characters -->
<!-- Arrows -->
<!ENTITY larr CDATA "←" -- leftwards arrow, U+2190 ISOnum -->
<!ENTITY uarr CDATA "↑" -- upwards arrow, U+2191 ISOnum-->
<!ENTITY rarr CDATA "→" -- rightwards arrow, U+2192 ISOnum -->
<!ENTITY darr CDATA "↓" -- downwards arrow, U+2193 ISOnum -->
<!ENTITY harr CDATA "↔" -- left right arrow, U+2194 ISOamsa -->
<!ENTITY crarr CDATA "↵" -- downwards arrow with corner leftwards
= carriage return, U+21B5 NEW -->
<!ENTITY lArr CDATA "⇐" -- leftwards double arrow, U+21D0 ISOtech -->
<!-- ISO 10646 does not say that lArr is the same as the 'is implied by' arrow
but also does not have any other character for that function. So ? lArr can
be used for 'is implied by' as ISOtech suggests -->
<!ENTITY uArr CDATA "⇑" -- upwards double arrow, U+21D1 ISOamsa -->
<!ENTITY rArr CDATA "⇒" -- rightwards double arrow,
U+21D2 ISOtech -->
<!-- ISO 10646 does not say this is the 'implies' character but does not have
another character with this function so ?
rArr can be used for 'implies' as ISOtech suggests -->
<!ENTITY dArr CDATA "⇓" -- downwards double arrow, U+21D3 ISOamsa -->
<!ENTITY hArr CDATA "⇔" -- left right double arrow,
U+21D4 ISOamsa -->
<!-- Mathematical Operators -->
<!ENTITY forall CDATA "∀" -- for all, U+2200 ISOtech -->
<!ENTITY part CDATA "∂" -- partial differential, U+2202 ISOtech -->
<!ENTITY exist CDATA "∃" -- there exists, U+2203 ISOtech -->
<!ENTITY empty CDATA "∅" -- empty set = null set = diameter,
U+2205 ISOamso -->
<!ENTITY nabla CDATA "∇" -- nabla = backward difference,
U+2207 ISOtech -->
<!ENTITY isin CDATA "∈" -- element of, U+2208 ISOtech -->
<!ENTITY notin CDATA "∉" -- not an element of, U+2209 ISOtech -->
<!ENTITY ni CDATA "∋" -- contains as member, U+220B ISOtech -->
<!-- should there be a more memorable name than 'ni'? -->
<!ENTITY prod CDATA "∏" -- n-ary product = product sign,
U+220F ISOamsb -->
<!-- prod is NOT the same character as U+03A0 'greek capital letter pi' though
the same glyph might be used for both -->
<!ENTITY sum CDATA "∑" -- n-ary sumation, U+2211 ISOamsb -->
<!-- sum is NOT the same character as U+03A3 'greek capital letter sigma'
though the same glyph might be used for both -->
<!ENTITY minus CDATA "−" -- minus sign, U+2212 ISOtech -->
<!ENTITY lowast CDATA "∗" -- asterisk operator, U+2217 ISOtech -->
<!ENTITY radic CDATA "√" -- square root = radical sign,
U+221A ISOtech -->
<!ENTITY prop CDATA "∝" -- proportional to, U+221D ISOtech -->
<!ENTITY infin CDATA "∞" -- infinity, U+221E ISOtech -->
<!ENTITY ang CDATA "∠" -- angle, U+2220 ISOamso -->
<!ENTITY and CDATA "∧" -- logical and = wedge, U+2227 ISOtech -->
<!ENTITY or CDATA "∨" -- logical or = vee, U+2228 ISOtech -->
<!ENTITY cap CDATA "∩" -- intersection = cap, U+2229 ISOtech -->
<!ENTITY cup CDATA "∪" -- union = cup, U+222A ISOtech -->
<!ENTITY int CDATA "∫" -- integral, U+222B ISOtech -->
<!ENTITY there4 CDATA "∴" -- therefore, U+2234 ISOtech -->
<!ENTITY sim CDATA "∼" -- tilde operator = varies with = similar to,
U+223C ISOtech -->
<!-- tilde operator is NOT the same character as the tilde, U+007E,
although the same glyph might be used to represent both -->
<!ENTITY cong CDATA "≅" -- approximately equal to, U+2245 ISOtech -->
<!ENTITY asymp CDATA "≈" -- almost equal to = asymptotic to,
U+2248 ISOamsr -->
<!ENTITY ne CDATA "≠" -- not equal to, U+2260 ISOtech -->
<!ENTITY equiv CDATA "≡" -- identical to, U+2261 ISOtech -->
<!ENTITY le CDATA "≤" -- less-than or equal to, U+2264 ISOtech -->
<!ENTITY ge CDATA "≥" -- greater-than or equal to,
U+2265 ISOtech -->
<!ENTITY sub CDATA "⊂" -- subset of, U+2282 ISOtech -->
<!ENTITY sup CDATA "⊃" -- superset of, U+2283 ISOtech -->
<!-- note that nsup, 'not a superset of, U+2283' is not covered by the Symbol
font encoding and is not included. Should it be, for symmetry?
It is in ISOamsn -->
<!ENTITY nsub CDATA "⊄" -- not a subset of, U+2284 ISOamsn -->
<!ENTITY sube CDATA "⊆" -- subset of or equal to, U+2286 ISOtech -->
<!ENTITY supe CDATA "⊇" -- superset of or equal to,
U+2287 ISOtech -->
<!ENTITY oplus CDATA "⊕" -- circled plus = direct sum,
U+2295 ISOamsb -->
<!ENTITY otimes CDATA "⊗" -- circled times = vector product,
U+2297 ISOamsb -->
<!ENTITY perp CDATA "⊥" -- up tack = orthogonal to = perpendicular,
U+22A5 ISOtech -->
<!ENTITY sdot CDATA "⋅" -- dot operator, U+22C5 ISOamsb -->
<!-- dot operator is NOT the same character as U+00B7 middle dot -->
<!-- Miscellaneous Technical -->
<!ENTITY lceil CDATA "⌈" -- left ceiling = apl upstile,
U+2308 ISOamsc -->
<!ENTITY rceil CDATA "⌉" -- right ceiling, U+2309 ISOamsc -->
<!ENTITY lfloor CDATA "⌊" -- left floor = apl downstile,
U+230A ISOamsc -->
<!ENTITY rfloor CDATA "⌋" -- right floor, U+230B ISOamsc -->
<!ENTITY lang CDATA "〈" -- left-pointing angle bracket = bra,
U+2329 ISOtech -->
<!-- lang is NOT the same character as U+003C 'less than'
or U+2039 'single left-pointing angle quotation mark' -->
<!ENTITY rang CDATA "〉" -- right-pointing angle bracket = ket,
U+232A ISOtech -->
<!-- rang is NOT the same character as U+003E 'greater than'
or U+203A 'single right-pointing angle quotation mark' -->
<!-- Geometric Shapes -->
<!ENTITY loz CDATA "◊" -- lozenge, U+25CA ISOpub -->
<!-- Miscellaneous Symbols -->
<!ENTITY spades CDATA "♠" -- black spade suit, U+2660 ISOpub -->
<!-- black here seems to mean filled as opposed to hollow -->
<!ENTITY clubs CDATA "♣" -- black club suit = shamrock,
U+2663 ISOpub -->
<!ENTITY hearts CDATA "♥" -- black heart suit = valentine,
U+2665 ISOpub -->
<!ENTITY diams CDATA "♦" -- black diamond suit, U+2666 ISOpub -->
24.4 Character entity references for markup-significant and
internationalization characters
The character entity references in this section are for escaping
markup-significant characters (these are the same as those in HTML 2.0
and 3.2), for denoting spaces and dashes. Other characters in this
section apply to internationalization issues such as the
disambiguation of bidirectional text (see the section on bidirectional
text for details).
Entities have also been added for the remaining characters occurring
in CP-1252 which do not occur in the HTMLlat1 or HTMLsymbol entity
sets. These all occur in the 128 to 159 range within the CP-1252
charset. These entities permit the characters to be denoted in a
platform-independent manner.
To support these entities, user agents may support full [ISO10646] or
use other means. Display of glyphs for these characters may be
obtained by being able to display the relevant [ISO10646] characters
or by other means, such as internally mapping the listed entities,
numeric character references, and characters to the appropriate
position in some font that contains the requisite glyphs.
24.4.1 The list of characters
<!-- Special characters for HTML -->
<!-- Character entity set. Typical invocation:
<!ENTITY % HTMLspecial PUBLIC
"-//W3C//ENTITIES Special//EN//HTML">
%HTMLspecial; -->
<!-- Portions © International Organization for Standardization 1986:
Permission to copy in any form is granted for use with
conforming SGML systems and applications as defined in
ISO 8879, provided this notice is included in all copies.
-->
<!-- Relevant ISO entity set is given unless names are newly introduced.
New names (i.e., not in ISO 8879 list) do not clash with any
existing ISO 8879 entity names. ISO 10646 character numbers
are given for each character, in hex. CDATA values are decimal
conversions of the ISO 10646 values and refer to the document
character set. Names are ISO 10646 names.
-->
<!-- C0 Controls and Basic Latin -->
<!ENTITY quot CDATA """ -- quotation mark = APL quote,
U+0022 ISOnum -->
<!ENTITY amp CDATA "&" -- ampersand, U+0026 ISOnum -->
<!ENTITY lt CDATA "<" -- less-than sign, U+003C ISOnum -->
<!ENTITY gt CDATA ">" -- greater-than sign, U+003E ISOnum -->
<!-- Latin Extended-A -->
<!ENTITY OElig CDATA "Œ" -- latin capital ligature OE,
U+0152 ISOlat2 -->
<!ENTITY oelig CDATA "œ" -- latin small ligature oe, U+0153 ISOlat2 -->
<!-- ligature is a misnomer, this is a separate character in some languages -->
<!ENTITY Scaron CDATA "Š" -- latin capital letter S with caron,
U+0160 ISOlat2 -->
<!ENTITY scaron CDATA "š" -- latin small letter s with caron,
U+0161 ISOlat2 -->
<!ENTITY Yuml CDATA "Ÿ" -- latin capital letter Y with diaeresis,
U+0178 ISOlat2 -->
<!-- Spacing Modifier Letters -->
<!ENTITY circ CDATA "ˆ" -- modifier letter circumflex accent,
U+02C6 ISOpub -->
<!ENTITY tilde CDATA "˜" -- small tilde, U+02DC ISOdia -->
<!-- General Punctuation -->
<!ENTITY ensp CDATA " " -- en space, U+2002 ISOpub -->
<!ENTITY emsp CDATA " " -- em space, U+2003 ISOpub -->
<!ENTITY thinsp CDATA " " -- thin space, U+2009 ISOpub -->
<!ENTITY zwnj CDATA "‌" -- zero width non-joiner,
U+200C NEW RFC 2070 -->
<!ENTITY zwj CDATA "‍" -- zero width joiner, U+200D NEW RFC 2070 -->
<!ENTITY lrm CDATA "‎" -- left-to-right mark, U+200E NEW RFC 2070 -->
<!ENTITY rlm CDATA "‏" -- right-to-left mark, U+200F NEW RFC 2070 -->
<!ENTITY ndash CDATA "–" -- en dash, U+2013 ISOpub -->
<!ENTITY mdash CDATA "—" -- em dash, U+2014 ISOpub -->
<!ENTITY lsquo CDATA "‘" -- left single quotation mark,
U+2018 ISOnum -->
<!ENTITY rsquo CDATA "’" -- right single quotation mark,
U+2019 ISOnum -->
<!ENTITY sbquo CDATA "‚" -- single low-9 quotation mark, U+201A NEW -->
<!ENTITY ldquo CDATA "“" -- left double quotation mark,
U+201C ISOnum -->
<!ENTITY rdquo CDATA "”" -- right double quotation mark,
U+201D ISOnum -->
<!ENTITY bdquo CDATA "„" -- double low-9 quotation mark, U+201E NEW -->
<!ENTITY dagger CDATA "†" -- dagger, U+2020 ISOpub -->
<!ENTITY Dagger CDATA "‡" -- double dagger, U+2021 ISOpub -->
<!ENTITY permil CDATA "‰" -- per mille sign, U+2030 ISOtech -->
<!ENTITY lsaquo CDATA "‹" -- single left-pointing angle quotation mark,
U+2039 ISO proposed -->
<!-- lsaquo is proposed but not yet ISO standardized -->
<!ENTITY rsaquo CDATA "›" -- single right-pointing angle quotation mark,
U+203A ISO proposed -->
<!-- rsaquo is proposed but not yet ISO standardized -->
<!ENTITY euro CDATA "€" -- euro sign, U+20AC NEW -->
Appendix A: Changes
Contents
1. Changes between 24 April 1998 HTML 4.0 and 24 December 1999 HTML
4.01 versions
1. Changes to the specification
o General changes
o On SGML and HTML
o HTML Document Representation
o Basic HTML data types
o Global structure of an HTML document
o Language information and text direction
o Tables
o Links
o Objects, Images, and Applets
o Style Sheets in HTML Documents
o Frames
o Forms
o SGML Declaration
o Strict DTD
o Notes
o References
2. Errors that were corrected
3. Minor typographical errors that were corrected
4. Clarifications
5. Known Browser problems
2. Changes between 18 December 1997 and 24 April 1998 versions
1. Errors that were corrected
2. Minor typographical errors that were corrected
3. Changes between HTML 3.2 and HTML 4.0 (18 December 1997)
1. Changes to elements
o New elements
o Deprecated elements
o Obsolete elements
2. Changes to attributes
3. Changes for accessibility
4. Changes for meta data
5. Changes for text
6. Changes for links
7. Changes for tables
8. Changes for images, objects, and image maps
9. Changes for forms
10. Changes for style sheets
11. Changes for frames
12. Changes for scripting
13. Changes for internationalization
A.1 Changes between 24 April 1998 HTML 4.0 and 24 December 1999 HTML 4.01
versions
This section describes how the 24 December 1999 version of the HTML
4.01 specification differs from the 24 April 1998 version of the HTML
4.0 specification.
A.1.1 Changes to the specification
General changes
* New style sheets for the document based on W3C technical report
styles.
* Added a short table of contents.
* Updated the copyright.
* Fixed document scripts to remove markup causing crashes on some
browsers.
* Thanks to Shane McCarron added to the acknowledgments.
* In section 1.4, removed copyright details and refer to W3C site
instead.
* References to the document character set are all ISO 10646 (and
one time to UNICODE to signal equivalence). References to UNICODE
refer only to the bidirectionality algorithm.
* Examples now use dated FPIs.
On SGML and HTML
* Section 3.2.2: Attribute values may contain colons and underscores
as well.
HTML Document Representation
* The Document Character Set: [ISO10646] now used only for
references to the document character set. [UNICODE] is reserved
for bidi-related references.
Basic HTML data types
* Media descriptors: All characters in examples now described using
hex notation (and reference to ISO 10646 rather than Unicode).
Global structure of an HTML document
* 7.2 HTML version information: Add a note about the HTML WG's
commitment that
+ Any changes to future HTML 4 DTDs will not invalidate
documents that conform to the DTDs of the present
specification. The HTML Working Group reserves the right to
correct known bugs.
+ Software conforming to the DTDs of the present specification
may ignore features of future HTML 4 DTDs that it does not
recognize.
* 7.2 HTML version information: Use undated, HTML 4 URIs for system
identifiers. These URIs are also used globally in all examples.
* 7.4.4 Meta data: Removed note about ongoing work at W3C on meta
data and replaced with a note about RDF.
* 7.4.4.2 Meta data: At the end of the section on HTTP headers,
removed the auto-refresh example (since not part of the
Recommendation) and added a note to use server-side redirects.
Language information and text direction
* The dir attribute: Clarification that dir applies to element
content, attribute values, and table direction.
Tables
* 11.2.6 Table Cells: The definitions of rowspan and colspan
changed. Now spans are bounded by groups (rowgroups or colgroups).
* 11.3.2 Table Cells: When "char=align" not supported by the user
agent, behavior is undefined.
Links
* 12.2 The A element: The description of the type attribute for the
A and (LINK) elements has been modified to emphasize its advisory
nature.
* 12.2.3 Anchors with the id attribute: It is legal for "name" and
"id" to appear in the same start tag when they are both defined
for an element. They must have identical values.
* 12.3.3 Links and search engines: Removed reference to dir
attribute in example since it doesn't apply to linked resources
(only element content and attribute text values).
* 12.4.1 Resolving relative URIs: Since RFC 2616 does not include a
Link header field, the following statement is qualified for
earlier versions of HTTP 1.1: "Link elements specified by HTTP
headers are handled exactly as LINK elements that appear
explicitly in a document."
Objects, Images, and Applets
* 13.2 The IMG element: Addition of the name attribute for backwards
compatibility.
* 13.2 The IMG element: Added a note that user agents must provide
different mechanisms for accessing the "longdesc" URI (of IMG) and
the "src" URI (of A) when an IMG is part of the content of an A
element.
* 13.3 The OBJECT element: Added a note that when the value of
"type" for OBJECT and the Content-Type HTTP header differ, the
latter takes precedence.
* 13.3 The OBJECT element: Added a statement to use PARAM instead of
the "data" and "classid" attributes for OBJECT together.
* 13.4 The APPLET element: Added a note that, for security reasons
only subdirectories are searched for the "codebase" attribute of
APPLET.
* 13.6.1 Client-side image maps: The definition of the "poly"
attribute has been cleared up. There is a note that if not closed
by authors, user agents should close the polygon for the "coords"
attribute of AREA.
* 13.6.1 Client-side image maps:
+ The content model of the MAP element now allows authors to
mix AREA content and block-level content.
+ User agents "should" render block-level content (used to be
"may").
+ The MAP element may be used without an image for general
purpose navigation tools.
+ User agents must ignore AREA elements when content is mixed
(AREA and block level).
+ Authors should specify geometries completely with either AREA
elements, or A elements in block content, or both.
* 13.7.2 and 13.7.3 : The vspace and hspace attribute definitions
now look like the definitions of other attributes.
* 13.7.2 and 13.7.3 : The type of vspace, hspace, and border
attribute values was changed from "length" to "pixels".
* 13.8 Alternate text: The last sentence of section now links to
notes for user agent developers for handling empty "alt" attribute
text.
Style Sheets in HTML Documents
* 14.6 Linking to style sheets with HTTP headers: Since RFC 2616
does not include a Link header field, the entire section is
qualified to pertain only to earlier versions of HTTP 1.1.
Frames
* 16.4.1 NOFRAMES: Added text to the NOFRAMES description about
rendering when (1) frames turned off (2) frames not supported.
* 16.4.1 NOFRAMES: Added text about which DTDs may have NOFRAMES
(frames, transitional).
Forms
* 17.2.1 Control types: In the description of radio buttons, when no
radio button is initially selected, user agent behavior for
selecting one is undefined. This differs from RFC 1866.
* 17.3 The FORM element: Addition of the name attribute for
backwards compatibility.
* 17.3 The FORM element: Removed the reference to the "mailto" URI
in the "action" attribute definition.
* 17.3 The FORM element: Removed "mailto" example near end of
section since behavior not defined in this spec.
* 17.3 The FORM element: The accept attribute is added to the DTD
fragment. Also, the description of the accept-charset attribute is
amended.
* 17.4 The INPUT element: Added missing "ismap" for the INPUT
element. Also, in definition of value., add "checkbox" to values
of type that require a value.
* 17.6.1: When no option is preselected, user agent behavior is
undefined. Authors should supply and explicit none option to cover
this case. This behavior differs from RFC 1866.
SGML Declaration
* SGML Declaration of HTML 4: Removed text about up-to-date
references to ISO 10646. Replaced with: "Revisions of the HTML 4
specification may update the reference to ISO 10646 to include
additional changes."
Strict DTD
* vspace/hspace/border attributes for IMG, OBJECT, APPLET in pixels.
* Changed content model of MAP to ((%block;) | AREA)+
* Added "ismap" attribute to INPUT
* The accept attribute is added to the DTD fragment for the FORM
element.
* The axis attribute comment has been changed to refer to a
comma-separated list.
* The archive attribute for the OBJECT element takes a value of type
CDATA instead of type %URI since the value is a space-separated
list of URIs.
Notes
* Notes Updated notes on accessibility to point to Web Content
Accessibility Guidelines.
References
* Updated links to RFCs to use http://www.ietf.org/rfc
* Put links in titles.
* Added revised date of 27 Aug 1998 for [DATETIME]
* Added revised date of 11 Jan 1999 for [CSS1].
* Publication date of [CSS2] fixed.
* [UNICODE] has been updated to version 3.0
* [ISO10646] has been updated to allow for new character
assignments. Note that amendment five is specifically taken into
account.
* [RFC1766] expected to be updated.
* [RFC2279] obsoletes [RFC2044].
* [RFC2616] obsoletes [RFC2068].
* [RFC2388] added in addition to [RFC1867].
* [LEXHTML] address updated, date added.
* [DCORE] address updated.
* Updated [WEBSGML]
* [HTML3STYLE] address updated.
* Added [RDF10] (replaced old RDF)
* Changed [WAIGUIDE] -> [WAI]
* Added informative references [WCGL], [UAGL], and [ATGL]
* Updated URI reference to [URI] (RFC 2396).
A.1.2 Errors that were corrected
Section 13.6.1
Image map examples using "poly" have been fixed to form a
closed polygon. Also, the last pair of coordinates is the same
as the first to close the polygon.
Section 14.4.1
In the final example, the STYLE element is missing the
attribute assignment "media=screen, print".
Section 15.2.1
In the example with "mypar", the CSS rule should read
P#mypar {font-style: italic; color: blue}
In CSS, "#" refers to an ID name while the "." refers to a
class name. This example is dealing with the "id" attribute.
Section 16.2.2
Values for marginwidth and marginheight must be 0 pixels or
more, not 1 pixel or more.
Section 16.2.2
The FRAME element does not take the target attribute.
Section 16.5
The IFRAME element does not take the target attribute.
Section 17.2.1
In the description of "checkboxes", change "selected" to
"checked" in "when the control element's selected attribute is
set."
Section 17.6.1
In the "Attributes defined elsewhere" section for the OPTGROUP
element, the attributes onfocus, onblur, and onchange should
not be there.
Section 18.2.3
To the list of elements that take onfocus and onblur, add A and
AREA.
Section 20
The SGML Declaration for HTML 4 must be modified slightly to
support hexadecimal numeric character references. The lines:
DELIM
GENERAL SGMLREF
SHORTREF SGMLREF
must be changed to:
DELIM
GENERAL SGMLREF
HCRO "&#x" -- 38 is the number for ampersand --
SHORTREF SGMLREF
And the initial <!SGML "ISO 8879:1986" must be changed to
<!SGML "ISO 8879:1986 (WWW)".
Section 21
The HR element should also take the lang and dir attributes.
These are noted as being defined elsewhere at the element's
definition, but were left out of the DTDs.
Section 21
The OBJECT element's archive attribute is defined in the DTD as
taking a value of type %URI". This is incorrect: the value may
be a space-separated list of URIs (as indicated in the
definition of the attribute and in the DTD comment).
The FORM element's DTD fragment should include a definition for
the accept attribute, which is listed in the element's
definition. The definition should be the following:
accept %ContentTypes; #IMPLIED -- list of MIME types for file upload --
Section B.4.1
At the end of the section, the following sentences are
incorrect: "The list of terms in the content is ALL, INDEX,
NOFOLLOW, NOINDEX. The name and the content attribute values
are case-insensitive." In fact, the META definition specifies
that values for the name and content attributes are
case-sensitive.
Section B.4.1.1
The specification reads, "Blank lines are not permitted." Blank
lines are permitted in the robots.txt file, just not within a
single "record". Note that the specification doesn't define
record.
Further down the page, the specification reads, "There must be
exactly one "User-agent" field per record." In fact, there can
be more than one User-Agent field in the robots.txt file, just
not more than one per record.
For information about search robots, please consult, for
example:
+ http://www.kollar.com/robots.html
+ http://info.webcrawler.com/mak/projects/robots/norobots-rfc.h
tml
+ http://info.webcrawler.com/mak/projects/robots/robots.html
References
+ The [URI] reference should be updated to RFC 2396 as of
August 1998. "Uniform Resource Identifiers (URI): Generic
Syntax", T. Berners-Lee, R. Fielding, L. Masinter, August
1998. RFC 2396 updates [RFC1738] and [RFC1808].
A.1.3 Minor typographical errors that were corrected
Section 2.1.1
The phrase "accessible via the path "/TR/REC-html4/". should
end with "/TR/REC-html40/".
Section 2.1.3
In the third bullet, the word "applets" should be "applet".
Section 3.3
In bullet two, the sentence "Whether the element's end tag is
optional." should read "Whether the element's tags are
optional."
Section 3.2.1
In the sentence beginning "Please consult the SGML standard",
the phrase "an end tag closes all omitted start tags up to the
matching start tag (section 7.5.1)" should read "an end tag
closes, back to the matching start tag, all unclosed
intervening start tags with omitted end tags".
Section 3.2.2
"Attribute names are always case-insensitive" is missing a
final period.
Section 3.3.4.2
The example with the OPTION element has an improper end tag; it
should be </OPTION>.
Later in the section, the sentence that begins "Authors should
be aware than" should say "aware that" instead.
Section 5.2.2
Change "ASCII characters" to ASCII-valued bytes".
Section 5.3.1
The second bullet should read "a" instead of "an" in "where H
is an hexadecimal number".
Section 6.5.1
The first sentence needs the indefinite article "a" before the
word "document".
Section 6.10
The first sentence needs the indefinite article "a" before the
word "single".
Section 6.12
Under "Next", "in an linear" should read "in a linear" instead.
Section 6.16
Change "cancelling" to "canceling".
Section 7.4.4.3
In the paragraph beginning "The scheme attribute allows...",
replace "Month-Date-Year" with "Month-Day-Year".
Section 7.5.4
In the sentence after the example, make "declaration" plural.
Section 7.5.6
For the ADDRESS element, in the section "Attributes defined
elsewhere", style and title are missing.
Also, after the section on "Attributes defined elsewhere", in
"contact information for document", put "a" before "document".
Section 8.2.3
In "Authors may also use special Unicode characters to achieve
multiply" change to "multiple" at the end.
Section 11.2.4.1
The sentence "The first COL element refers to the first 39
columns (doing nothing special to them) and the second one
assigns an id value to the fortieth columns so that style
sheets may refer to it." should have "fortieth column" instead.
Section 11.2.5
For the TR element, in the section "Attributes defined
elsewhere", bgcolor is missing.
Section 11.2.6
For the TH and TD elements, the type of the width and height
attributes is changed from "%Pixels;" to "%Length;" to allow
for percentage values.
Section 11.3.1
In the first sentence of the frame attribute definition, use
"surrounding" instead of "that surrounds".
Section 11.4.1
First bullet, third sentence. "Note that its not always
possible" should have "it's" instead.
Section 12.1.2
The last sentence should read "Further information is given
below on using links for..." (change "of" to "on"). This
sentence is also missing its closing punctuation.
Section 12.2.2
The last paragraph should read "Since the DTD defines the LINK
element to be empty..." (insert definite article "the" before
"LINK").
Section 12.2.3
Just before section 12.2.4, the third bullet. "richer anchors
names" should read "richer anchor names".
Section 13.3.4
In the paragraph that begins "In the following example...", the
phrase "cause it so be instantiated" should be changed to cause
it to be instantiated" (change "so" to "to").
Section 13.4
Just after the deprecated example, the sentence "This example
may be rewritten as follows with OBJECT as follows:" should say
"This example may be rewritten with OBJECT as follows:".
Section 13.6.1
Under the "coords" attribute, the word "and" should be
substituted for the word "a" so the sentence reads, "This
attribute specifies the position and shape on the screen."
Section 13.7.1
In the definition of the height attribute, the phrase "Image
and object override" should read "Image and object height
override".
Section 15.1.3.1
Under the subheading "Float an object", in the first paragraph,
the first use of the word "object" should be "objects".
Section 15.1.3.2
In the "Deprecated" example, the first sentence should read "If
the clear attribute is set to left or all, the next line will
appear as follows:" ("the" before "next line").
Section 15.3
The align attribute for HR is not defined elsewhere.
Section 16.1
In the last sentence of the first paragraph, the word "though"
should be "through".
Section 16.3.1
In the second sentence, the word "factorizing" should be
"factoring".
Section 16.4.1
The list of "attributes defined elsewhere" was inadvertently
omitted after the definition of NOFRAMES. These attributes are:
class, id, lang, dir, title, style, and the %events;
attributes.
Section 17.1
In "(entering text, selecting menu items, etc.)", add the ","
after "text".
Section 17.5
In the paragraph that begins "Visual user agents may
render...", the indefinite article "a" should be removed from
before the word "flat".
Section 17.12.1
A comma should be added between BUTTON and INPUT in the list of
elements that support the "disabled" attribute.
Section 17.13.4.2
In the examples at the end of the section, change
"Content-Disposition: attachment" to "Content-Disposition:
file". Also, in an earlier example, change "server.dom" to
"server.com".
Section 18.2.2.1
After the first example, the indefinite article before
"content-type" needs to be "a", not "an". The same applies to
"content-type" in the next paragraph.
In the sentence beginning "Documents that do not specify...",
the indefinite article "a" needs to be removed from before
"default scripting language information".
Section 18.2.3
In the first sentence of the first note, the word "realm"
should be preceded by the definite article "the".
Section 18.3.1
In the second sentence of the first paragraph, the word "be"
needs to be inserted between the words "only" and "rendered".
Section 21
+ In all DTDs, under the COLGROUP element, the content model
should indicate "COL", not "col".
+ In the comment about the %Scope entity, change "axes" to
"headers" attribute.
Section 24.2.1
At end of definition of "thorn", remove stray final word.
Section 24.4
Change "cp-1252" to "CP-1252".
Appendix: Changes for tables
In the paragraph on the COLGROUP element, the last sentence
should read: "The semantics of COLGROUP have been clarified
over previous drafts, and rules="basic" has been replaced by
rules="groups"."
Changes to elements
The list of deprecated elements should include S.
Section B.3.2
In "delimiter followed by a name character", change to
delimiter followed by a name start character".
Section B.4
Under "Provide keywords and descriptions", the middle of the
sentence "The value of the name attribute sought by a search
attribute is not defined by this specification." should read
"search engine" instead.
Section B.4
In the example to indicate the beginning of a collection
replace rel="begin" with rel="start".
Section B.4.1
Remove "The name and the content attribute values are
case-insensitive."
Section B.5.1.2
The last sentence of the last paragraph is missing a closing
parenthesis.
Section B.7.1.1
In the deprecated example:
<BODY bgcolor='&{randomrgb};'>
The word "randomrbg" should be "randomrgb".
A.1.4 Clarifications
Section 3.2.1
In seventh paragraph, added "back to the matching start tag" to
"(e.g., they must be properly nested, an end tag closes, back
to the matching start tag, all unclosed intervening start tags
with omitted end tags (section 7.5.1), etc.)."
Section 3.2.4
Added a statement that comments are markup.
Section 3.3.3
In the second list item, change "Whether the element's end tag"
to "Whether the element's tags".
Section 3.3.3.1
In a content model definition, "A" means that "A" must occur
one time and only one time. Also, added "+(A)" and "-(A)" to
the section on content model syntax.
Section 7.4.2
Clarified that TITLE may not include comments.
Section 10.3
All uses of "cracker" in this section and its subsections are
replaced with "hacker". Also, definitions of "hacker" and
"nerd" taken from "The Hacker's Dictionary".
Section 13.7.2
The hspace and vspace attributes are deprecated.
Section 13.7.4
The align attribute is deprecated for IMG, OBJECT, and APPLET.
A.1.5 Known Browser problems
* Some versions of Netscape Navigator 4.0X crash upon reading
Chapter 3 of previous versions of this specification. Netscape is
aware of this bug and have fixed it in version 4.5. To work around
this bug, go to the Edit/Preferences/Advanced submenu and disable
Style Sheets (and possibly JavaScript).
A.2 Changes between 18 December 1997 and 24 April 1998 versions
This section describes how the 24 April 1998 version of the HTML 4.0
specification differs from the 18 December 1997 version.
A.2.1 Errors that were corrected
Section 2.1.1
"http://www.w3.org/TR/PR-html4/cover.html" was said to
designate the current HTML specification. The current HTML
specification is actually at http://www.w3.org/TR/REC-html40.
Section 7.5.2
The hypertext link on name was incorrect. It now links to
types.html#type-name.
Section 7.5.4
href was listed as an attribute of the DIV and SPAN elements.
It is not.
Section 7.5.6
A P element was used in the example. It is invalid in ADDRESS.
Section 8.1
In the first example, which reads "Her super-powers were the
result...", there was an extra double quote mark before the
word "Her".
Section 9.3.4
The attribute width was not noted as deprecated.
Section 11.2.4, "Calculating the width of columns"
The sentence "We have set the value of the align attribute in
the third column group to 'center'" read "second" instead of
"third".
Section 11.2.6, "Cells that span several rows or columns"
The second paragraph read "In this table definition, we specify
that the cell in row four, column two should span a total of
three columns, including the current row." It now ends
"...including the current column."
Section 13.2
The sentence beginning "User agents must render alternate text
when they cannot support ..." read "next", instead of "text".
Section 13.6.2
The last sentence of the second paragraph applied to both the
IMG and INPUT elements. However, the ismap attribute is not
defined for INPUT. The sentence now only applies to IMG.
Section 14.2.3
The title attribute for the STYLE element was not listed as an
attribute defined elsewhere.
Section 14.3.2
The second example set title="Compact". It now sets
title="compact".
Section 15.1.2
The sentence ending "the align attribute." read "the align
element."
Section 15.1.3.2
The CSS style rule "BR.mybr { clear: left }" was incorrect,
since it refers to the class "mybr" and not the id value. The
correct syntax is: "BR#mybr { clear: left }".
Section 16
All the examples containing a Document Type Declaration used
something like "THE_LATEST_VERSION_/frameset.dtd" or
"THE_LATEST_VERSION_" as the system identifier for the Frameset
DTD. They now use the proper document type declaration
indicated in Section 7.2
Section 16.3 and Section 16.3.1
The second example of 16.3 and the example of 16.3.1 used the
wrong DTD; they now use the Transitional DTD.
Section 17.5
In "attributes defined elsewhere" for the BUTTON element, id,
class, lang, dir, title, style, and tabindex were missing.
Also, usemap has been removed.
Section 17.6/17.6.1
The "attributes defined elsewhere" for OPTION and OPTGROUP
mistakenly listed onfocus, onblur, and onchange. The
"attributes defined elsewhere" section was missing for the
SELECT element (please see the DTD for the full list of
attributes).
Section 17.9.1
The tabindex attribute was said to be defined for the LABEL
element. It is not.
Section 17.12.2
The sentence "The following elements support the readonly
attribute: INPUT and TEXTAREA." read "The following elements
support the readonly attribute: INPUT, TEXT, PASSWORD, and
TEXTAREA."
Section 18.2.2, "Local declaration of a scripting language"
The first paragraph read: "It is also possible to specify the
scripting language in each SCRIPT element via the type
attribute. In the absence of a default scripting language
specification, this attribute must be set on each SCRIPT
element." Since the type attribute is required for the SCRIPT
element, this paragraph now reads: "The type attribute must be
specified for each SCRIPT element instance in a document. The
value of the type attribute for a SCRIPT element overrides the
default scripting language for that element."
Section 21
Added note that the spec includes some syntactic constraints
that cannot be expressed in the DTD.
Section 24.2.1 and file HTMLlat1.ent
The comment for the character reference "not" read "=
discretionary hyphen". This has been removed.
The FPI in comment read "-//W3C//ENTITIES Full Latin
1//EN//HTML", instead this is now "-//W3C//ENTITIES
Latin1//EN//HTML".
Section 24.3.1 and file HTMLsymbol.ent
The FPI in comment read "-//W3C//ENTITIES Symbolic//EN//HTML",
instead this is now "-//W3C//ENTITIES Symbols//EN//HTML".
Section A.1.1, "New elements" (previously A.1.1) and Section A.1.1,
"Deprecated elements" (previously A.1.2)
The S element which is deprecated was listed as part of the
changes between HTML 3.2 and HTML 4.0. This element was not
actually defined in HTML 3.2. It is now in the new elements
list.
Section A.1.3 (previously A.3)
The longdesc attribute was said to be specified for tables. It
is not. Instead, the summary attribute allows authors to give
longer descriptions of tables.
Section B.4
The sentence "You may help search engines by using the LINK
element with rel="start" along with the title attribute, ..."
read "You may help search engines by using the LINK element
with rel="begin" along with a TITLE, ..." The same stands for
the companion example.
Section B.5.1
The sentence "This can be altered by setting the width
attribute of the TABLE element." read "This can be altered by
setting the width-TABLE attribute of the TABLE element."
Section B.5.2
The sentence "Rules for handling objects too large for a column
apply when the explicit or implied alignment results in a
situation where the data exceeds the assigned width of the
column." read "too large for column". The meaning of the
sentence was unclear since it referred to "rules" governing an
error condition; user agent behavior in error conditions lies
outside the scope of the specification.
Index of attributes
The href attribute for the BASE element was marked as
deprecated. It is not. However, it is not defined in the
Strict DTD either.
The language attribute for the SCRIPT element was not marked as
deprecated. It is now, and it is no longer defined in the
Strict DTD.
A.2.2 Minor typographical errors that were corrected
Section 2.1.3
"Relative URIs are resolved ..." was "Relative URIsare resolved
...".
Section 2.2.1
The second word "of" was missing in "Despite never receiving
consensus in standards discussions, these drafts led to the
adoption of a range of new features."
Section 3.3.3
The sentence "Element types that are designed to have no
content are called empty elements." contained one too many
"elements". The word "a" was missing in the sentence "A few
HTML element types use an additional SGML feature to exclude
elements from a content model".
Also, in list item two, a period was missing between "optional"
and "Two".
Section 3.3.4
In the section on "Boolean attributes", the sentence that
begins "In HTML, boolean attributes may appear in minimized
..." included a bogus word "be".
Section 6.3
The sentence beginning "For introductory information about
attributes, ..." read "For introductory about attributes, ...".
Section 6.6
In the first sentence of the section on Pixels, "is an integer"
read "is integer".
Section 7.4.1
The first word "The" was missing at the beginning of the
section title.
Section 7.4.4
The last word "a" was missing in the sentence "The meaning of a
property and the set of legal values for that property should
be defined in a reference lexicon called profile."
Section 7.5.2
"Variable déclarée deux fois" read "Variable déclaré deux
fois".
Section 9.2.2
The language of the quotations was "en" instead of "en-us",
while in British English, the single quotation marks would
delimit the outer quotation.
Section 9.3.2
In the first line, the sixth character of "
" was the
letter 'O' instead of a zero.
Section 10.3.1
"(they are case-sensitive)" read "(the are case-sensitive)".
Section 12.1.1
In the sentence beginning "Note that the href attribute in each
source ..." the space was missing between "href" and
"attribute".
Section 12.1.2
The sentence "Links that express other types of relationships
have one or more link types specified in their source anchors."
read "Links that express other types of relationships have one
or more link type specified in their source anchor."
Section 12.1.5
The second paragraph reads "the hreflang attribute provides
user agents about the language of a ..." It should read "the
hreflang attribute provides user agents with information about
the language of a ..."
Section 13.3.2
In the sentence beginning "Any number of PARAM elements may
appear in the content of an OBJECT or APPLET element, ..." a
space was missing between "APPLET" and "element".
Section 14.2.2
There was a bogus word "style" at the beginning of the sentence
"The style attribute specifies ..."
Section 17.2
In "Those controls for which name/value pairs are submitted are
called successful controls" the word "for" was missing.
Section 17.10
There was a bogus word "/samp" just before section 17.11.
Section 17.11
The first sentence read, "In an HTML document, an element must
receive focus from the user in order to become active and
perform their tasks" (instead of "its" tasks).
Section 18.2.2
Just before section 18.2.3, the sentence that includes "a name
attribute takes precedence over an id if both are set." read
"over a id if both are set.".
Section 19.1
The section title read "document Document Validation". It now
is "Document Validation".
Section 21
The FPI for the Transitional HTML 4.0 DTD was missing a closing
double quote.
Section B.5.1/B.5.2
This sections referred to a non-existent cols attribute. This
attribute is not part of HTML 4.0. Calculating the number of
columns in a table is described in section Section 11.2.4.3, in
the chapter on tables. In sections B.5.1 and B.5.2, occurrences
of cols have been replaced by "the number of columns specified
by the COL and COLGROUP elements".
Section B.5.2
In the sentence "The values for the frame attribute have been
chosen to avoid clashes with the rules, align and valign
attributes." a space was missing between "the" and "frame" and
the last attribute was "valign-COLGROUP".
Section B.10.1
The last sentence read "Once a file is uploaded, the processing
agent should process and store the it appropriately." "the it"
was changed to "it".
Index of Elements
"strike-through" in the description of the S element read
"sstrike-through".
A.3 Changes between HTML 3.2 and HTML 4.0 (18 December 1997)
This section describes how the 18 December 1997 specification of HTML
4.0 differs from HTML 3.2 ([HTML32]).
A.3.1 Changes to elements
New elements
The new elements in HTML 4.0 are: ABBR, ACRONYM, BDO, BUTTON, COL,
COLGROUP, DEL, FIELDSET, FRAME, FRAMESET, IFRAME, INS, LABEL, LEGEND,
NOFRAMES, NOSCRIPT, OBJECT, OPTGROUP, PARAM, S (deprecated), SPAN,
TBODY, TFOOT, THEAD, and Q.
Deprecated elements
The following elements are deprecated: APPLET, BASEFONT, CENTER, DIR,
FONT, ISINDEX, MENU, S, STRIKE, and U.
Obsolete elements
The following elements are obsolete: LISTING, PLAINTEXT, and XMP. For
all of them, authors should use the PRE element instead.
A.3.2 Changes to attributes
* Almost all attributes that specify the presentation of an HTML
document (e.g., colors, alignment, fonts, graphics, etc.) have
been deprecated in favor of style sheets. The list of attributes
in the appendix indicates which attributes have been deprecated.
* The id and class attribute allow authors to assign name and class
information to elements for style sheets, as anchors, for
scripting, for object declarations, general purpose document
processing, etc.
A.3.3 Changes for accessibility
HTML 4.0 features many changes to promote accessibility, including:
* The title attribute may now be set on virtually every element.
* Authors may provide long descriptions of tables (see the summary
attribute), images and frames (see the longdesc attribute).
A.3.4 Changes for meta data
Authors may now specify profiles that provide explanations about meta
data specified with the META or LINK elements.
A.3.5 Changes for text
* New features for internationalization allow authors to specify
text direction and language.
* The INS and DEL elements allow authors to mark up changes in their
documents.
* The ABBR and ACRONYM elements allow authors to mark up
abbreviations and acronyms in their documents.
A.3.6 Changes for links
* The id attribute makes any element the destination anchor of a
link.
A.3.7 Changes for tables
The HTML 4.0 table model has grown out of early work on HTML+ and the
initial draft of HTML3.0. The earlier model has been extended in
response to requests from information providers as follows:
* Authors may specify tables that may be incrementally displayed as
the user agent receives data.
* Authors may specify tables that are more accessible to users with
non-visual user agents.
* Authors may specify tables with fixed headers and footers. User
agents may take advantage of these when scrolling large tables or
rendering tables to paged media.
The HTML 4.0 table model also satisfies requests for optional
column-based defaults for alignment properties, more flexibility in
specifying table frames and rules, and the ability to align on
designated characters. It is expected, however, that style sheets will
take over the task of rendering tables in the near future.
In addition, a major goal has been to provide backwards compatibility
with the widely deployed Netscape implementation of tables. Another
goal has been to simplify importing tables conforming to the SGML CALS
model. The latest draft makes the align attribute compatible with the
latest versions of the most popular browsers. Some clarifications have
been made to the role of the dir attribute and recommended behavior
when absolute and relative column widths are mixed.
A new element, COLGROUP, has been introduced to allow sets of columns
to be grouped with different width and alignment properties specified
by one or more COL elements. The semantics of COLGROUP have been
clarified over previous drafts, and rules="basic" has been replaced by
rules="groups".
The style attribute is included as a means for extending the
properties associated with edges and interiors of groups of cells. For
instance, the line style: dotted, double, thin/thick etc; the
color/pattern fill for the interior; cell margins and font
information. This will be the subject for a companion specification on
style sheets.
The frame and rules attributes have been modified to avoid SGML name
clashes with each other, and to avoid clashes with the align and
valign attributes. These changes were additionally motivated by the
desire to avoid future problems if this specification is extended to
allow frame and rules attributes with other table elements.
A.3.8 Changes for images, objects, and image maps
* The OBJECT element allows generic inclusion of objects.
* The IFRAME and OBJECT elements allow authors to create embedded
documents.
* The alt attribute is required on the IMG and AREA elements.
* The mechanism for creating image maps now allows authors to create
more accessible image maps. The content model of the MAP element
has changed for this reason.
A.3.9 Changes for forms
This specification introduces several new attributes and elements that
affect forms:
* The accesskey attribute allows authors to specify direct keyboard
access to form controls.
* The disabled attribute allows authors to make a form control
initially insensitive.
* The readonly attribute, allows authors to prohibit changes to a
form control.
* The LABEL element associates a label with a particular form
control.
* The FIELDSET element groups related fields together and, in
association with the LEGEND element, can be used to name the
group. Both of these new elements allow better rendering and
better interactivity. Speech-based browsers can better describe
the form and graphic browsers can make labels sensitive.
* A new set of attributes, in combination with scripts, allow form
providers to verify user-entered data.
* The BUTTON element and INPUT with type set to "button" can be used
in combination with scripts to create richer forms.
* The OPTGROUP element allows authors to group menu options together
in a SELECT, which is particularly important for form
accessibility.
* Additional changes for internationalization.
A.3.10 Changes for style sheets
HTML 4.0 supports a larger set of media descriptors so that authors
may write device-sensitive style sheets.
A.3.11 Changes for frames
HTML 4.0 supports frame documents and inline frames.
A.3.12 Changes for scripting
Many elements now feature event attributes that may be coupled with
scripts; the script is executed when the event occurs (e.g., when a
document is loaded, when the mouse is clicked, etc.).
A.3.13 Changes for internationalization
HTML 4.0 integrates the recommendations of [RFC2070] for the
internationalization of HTML.
However, this specification and [RFC2070] differ as follows:
* The accept-charset attribute has been specified for the FORM
element rather than the TEXTAREA and INPUT elements.
* The HTML 4.0 specification makes additional clarifications with
respect to the bidirectional algorithm.
* The use of CDATA to define the SCRIPT and STYLE elements does not
preserve the ability to transcode documents, as described in
section 2.1 of [RFC2070].
Appendix B: Performance, Implementation, and Design Notes
Contents
1. Notes on invalid documents
2. Special characters in URI attribute values
1. Non-ASCII characters in URI attribute values
2. Ampersands in URI attribute values
3. SGML implementation notes
1. Line breaks
2. Specifying non-HTML data
o Element content
o Attribute values
3. SGML features with limited support
4. Boolean attributes
5. Marked Sections
6. Processing Instructions
7. Shorthand markup
4. Notes on helping search engines index your Web site
1. Search robots
o The robots.txt file
o Robots and the META element
5. Notes on tables
1. Design rationale
o Dynamic reformatting
o Incremental display
o Structure and presentation
o Row and column groups
o Accessibility
2. Recommended Layout Algorithms
o Fixed Layout Algorithm
o Autolayout Algorithm
6. Notes on forms
1. Incremental display
2. Future projects
7. Notes on scripting
1. Reserved syntax for future script macros
o Current Practice for Script Macros
8. Notes on frames
9. Notes on accessibility
10. Notes on security
1. Security issues for forms
The following notes are informative, not normative. Despite the
appearance of words such as "must" and "should", all requirements in
this section appear elsewhere in the specification.
B.1 Notes on invalid documents
This specification does not define how conforming user agents handle
general error conditions, including how user agents behave when they
encounter elements, attributes, attribute values, or entities not
specified in this document.
However, to facilitate experimentation and interoperability between
implementations of various versions of HTML, we recommend the
following behavior:
* If a user agent encounters an element it does not recognize, it
should try to render the element's content.
* If a user agent encounters an attribute it does not recognize, it
should ignore the entire attribute specification (i.e., the
attribute and its value).
* If a user agent encounters an attribute value it doesn't
recognize, it should use the default attribute value.
* If it encounters an undeclared entity, the entity should be
treated as character data.
We also recommend that user agents provide support for notifying the
user of such errors.
Since user agents may vary in how they handle error conditions,
authors and users must not rely on specific error recovery behavior.
The HTML 2.0 specification ([RFC1866]) observes that many HTML 2.0
user agents assume that a document that does not begin with a document
type declaration refers to the HTML 2.0 specification. As experience
shows that this is a poor assumption, the current specification does
not recommend this behavior.
For reasons of interoperability, authors must not "extend" HTML
through the available SGML mechanisms (e.g., extending the DTD, adding
a new set of entity definitions, etc.).
B.2 Special characters in URI attribute values
B.2.1 Non-ASCII characters in URI attribute values
Although URIs do not contain non-ASCII values (see [URI], section 2.1)
authors sometimes specify them in attribute values expecting URIs
(i.e., defined with %URI; in the DTD). For instance, the following
href value is illegal:
<A href="http://foo.org/Håkon">...</A>
We recommend that user agents adopt the following convention for
handling non-ASCII characters in such cases:
1. Represent each character in UTF-8 (see [RFC2279]) as one or more
bytes.
2. Escape these bytes with the URI escaping mechanism (i.e., by
converting each byte to %HH, where HH is the hexadecimal notation
of the byte value).
This procedure results in a syntactically legal URI (as defined in
[RFC1738], section 2.2 or [RFC2141], section 2) that is independent
of the character encoding to which the HTML document carrying the URI
may have been transcoded.
Note. Some older user agents trivially process URIs in HTML using the
bytes of the character encoding in which the document was received.
Some older HTML documents rely on this practice and break when
transcoded. User agents that want to handle these older documents
should, on receiving a URI containing characters outside the legal
set, first use the conversion based on UTF-8. Only if the resulting
URI does not resolve should they try constructing a URI based on the
bytes of the character encoding in which the document was received.
Note. The same conversion based on UTF-8 should be applied to values
of the name attribute for the A element.
B.2.2 Ampersands in URI attribute values
The URI that is constructed when a form is submitted may be used as an
anchor-style link (e.g., the href attribute for the A element).
Unfortunately, the use of the "&" character to separate form fields
interacts with its use in SGML attribute values to delimit character
entity references. For example, to use the URI "http://host/?x=1&y=2"
as a linking URI, it must be written <A
href="http://host/?x=1&y=2"> or <A
href="http://host/?x=1&y=2">.
We recommend that HTTP server implementors, and in particular, CGI
implementors support the use of ";" in place of "&" to save authors
the trouble of escaping "&" characters in this manner.
B.3 SGML implementation notes
B.3.1 Line breaks
SGML (see [ISO8879], section 7.6.1) specifies that a line break
immediately following a start tag must be ignored, as must a line
break immediately before an end tag. This applies to all HTML elements
without exception.
The following two HTML examples must be rendered identically:
<P>Thomas is watching TV.</P>
<P>
Thomas is watching TV.
</P>
So must the following two examples:
<A>My favorite Website</A>
<A>
My favorite Website
</A>
B.3.2 Specifying non-HTML data
Script and style data may appear as element content or attribute
values. The following sections describe the boundary between HTML
markup and foreign data.
Note. The DTD defines script and style data to be CDATA for both
element content and attribute values. SGML rules do not allow
character references in CDATA element content but do allow them in
CDATA attribute values. Authors should pay particular attention when
cutting and pasting script and style data between element content and
attribute values.
This asymmetry also means that when transcoding from a richer to a
poorer character encoding, the transcoder cannot simply replace
unconvertible characters in script or style data with the
corresponding numeric character references; it must parse the HTML
document and know about each script and style language's syntax in
order to process the data correctly.
Element content
When script or style data is the content of an element (SCRIPT and
STYLE), the data begins immediately after the element start tag and
ends at the first ETAGO ("</") delimiter followed by a name start
character ([a-zA-Z]); note that this may not be the element's end tag.
Authors should therefore escape "</" within the content. Escape
mechanisms are specific to each scripting or style sheet language.
ILLEGAL EXAMPLE:
The following script data incorrectly contains a "</" sequence (as
part of "</EM>") before the SCRIPT end tag:
<SCRIPT type="text/javascript">
document.write ("<EM>This won't work</EM>")
</SCRIPT>
In JavaScript, this code can be expressed legally by hiding the ETAGO
delimiter before an SGML name start character:
<SCRIPT type="text/javascript">
document.write ("<EM>This will work<\/EM>")
</SCRIPT>
In Tcl, one may accomplish this as follows:
<SCRIPT type="text/tcl">
document write "<EM>This will work<\/EM>"
</SCRIPT>
In VBScript, the problem may be avoided with the Chr() function:
"<EM>This will work<" & Chr(47) & "EM>"
Attribute values
When script or style data is the value of an attribute (either style
or the intrinsic event attributes), authors should escape occurrences
of the delimiting single or double quotation mark within the value
according to the script or style language convention. Authors should
also escape occurrences of "&" if the "&" is not meant to be the
beginning of a character reference.
* '"' should be written as """ or """
* '&' should be written as "&" or "&"
Thus, for example, one could write:
<INPUT name="num" value="0"
onchange="if (compare(this.value, "help")) {gethelp()}">
B.3.3 SGML features with limited support
SGML systems conforming to [ISO8879] are expected to recognize a
number of features that aren't widely supported by HTML user agents.
We recommend that authors avoid using all of these features.
B.3.4 Boolean attributes
Authors should be aware that many user agents only recognize the
minimized form of boolean attributes and not the full form.
For instance, authors may want to specify:
<OPTION selected>
instead of
<OPTION selected="selected">
B.3.5 Marked Sections
Marked sections play a role similar to the #ifdef construct recognized
by C preprocessors.
<![INCLUDE[
<!-- this will be included -->
]]>
<![IGNORE[
<!-- this will be ignored -->
]]>
SGML also defines the use of marked sections for CDATA content, within
which "<" is not treated as the start of a tag, e.g.,
<![CDATA[
<an> example of <sgml> markup that is
not <painful> to write with < and such.
]]>
The telltale sign that a user agent doesn't recognize a marked section
is the appearance of "]]>", which is seen when the user agent
mistakenly uses the first ">" character as the end of the tag starting
with "<![".
B.3.6 Processing Instructions
Processing instructions are a mechanism to capture platform-specific
idioms. A processing instruction begins with <? and ends with >
<?instruction >
For example:
<?>
<?style tt = font courier>
<?page break>
<?experiment> ... <?/experiment>
Authors should be aware that many user agents render processing
instructions as part of the document's text.
B.3.7 Shorthand markup
Some SGML SHORTTAG constructs save typing but add no expressive
capability to the SGML application. Although these constructs
technically introduce no ambiguity, they reduce the robustness of
documents, especially when the language is enhanced to include new
elements. Thus, while SHORTTAG constructs of SGML related to
attributes are widely used and implemented, those related to elements
are not. Documents that use them are conforming SGML documents, but
are unlikely to work with many existing HTML tools.
The SHORTTAG constructs in question are the following:
* NET tags:
<name/.../
* closed Start Tag:
<name1<name2>
* Empty Start Tag:
<>
* Empty End Tag:
</>
B.4 Notes on helping search engines index your Web site
This section provides some simple suggestions that will make your
documents more accessible to search engines.
Define the document language
In the global context of the Web it is important to know which
human language a page was written in. This is discussed in the
section on language information.
Specify language variants of this document
If you have prepared translations of this document into other
languages, you should use the LINK element to reference these.
This allows an indexing engine to offer users search results in
the user's preferred language, regardless of how the query was
written. For instance, the following links offer French and
German alternatives to a search engine:
<LINK rel="alternate"
type="text/html"
href="mydoc-fr.html" hreflang="fr"
lang="fr" title="La vie souterraine">
<LINK rel="alternate"
type="text/html"
href="mydoc-de.html" hreflang="de"
lang="de" title="Das Leben im Untergrund">
Provide keywords and descriptions
Some indexing engines look for META elements that define a
comma-separated list of keywords/phrases, or that give a short
description. Search engines may present these keywords as the
result of a search. The value of the name attribute sought by a
search engine is not defined by this specification. Consider
these examples,
<META name="keywords" content="vacation,Greece,sunshine">
<META name="description" content="Idyllic European vacations">
Indicate the beginning of a collection
Collections of word processing documents or presentations are
frequently translated into collections of HTML documents. It is
helpful for search results to reference the beginning of the
collection in addition to the page hit by the search. You may
help search engines by using the LINK element with rel="start"
along with the title attribute, as in:
<LINK rel="start"
type="text/html"
href="page1.html"
title="General Theory of Relativity">
Provide robots with indexing instructions
People may be surprised to find that their site has been
indexed by an indexing robot and that the robot should not have
been permitted to visit a sensitive part of the site. Many Web
robots offer facilities for Web site administrators and content
providers to limit what the robot does. This is achieved
through two mechanisms: a "robots.txt" file and the META
element in HTML documents, described below.
B.4.1 Search robots
The robots.txt file
When a Robot visits a Web site, say http://www.foobar.com/, it firsts
checks for http://www.foobar.com/robots.txt. If it can find this
document, it will analyze its contents to see if it is allowed to
retrieve the document. You can customize the robots.txt file to apply
only to specific robots, and to disallow access to specific
directories or files.
Here is a sample robots.txt file that prevents all robots from
visiting the entire site
User-agent: * # applies to all robots
Disallow: / # disallow indexing of all pages
The Robot will simply look for a "/robots.txt" URI on your site, where
a site is defined as a HTTP server running on a particular host and
port number. Here are some sample locations for robots.txt:
Site URI URI for robots.txt
http://www.w3.org/ http://www.w3.org/robots.txt
http://www.w3.org:80/ http://www.w3.org:80/robots.txt
http://www.w3.org:1234/ http://www.w3.org:1234/robots.txt
http://w3.org/ http://w3.org/robots.txt
There can only be a single "/robots.txt" on a site. Specifically, you
should not put "robots.txt" files in user directories, because a robot
will never look at them. If you want your users to be able to create
their own "robots.txt", you will need to merge them all into a single
"/robots.txt". If you don't want to do this your users might want to
use the Robots META Tag instead.
Some tips: URI's are case-sensitive, and "/robots.txt" string must be
all lower-case. Blank lines are not permitted within a single record
in the "robots.txt" file.
There must be exactly one "User-agent" field per record. The robot
should be liberal in interpreting this field. A case-insensitive
substring match of the name without version information is
recommended.
If the value is "*", the record describes the default access policy
for any robot that has not matched any of the other records. It is not
allowed to have multiple such records in the "/robots.txt" file.
The "Disallow" field specifies a partial URI that is not to be
visited. This can be a full path, or a partial path; any URI that
starts with this value will not be retrieved. For example,
Disallow: /help disallows both /help.html and /help/index.html, whereas
Disallow: /help/ would disallow /help/index.html but allow /help.html.
An empty value for "Disallow", indicates that all URIs can be
retrieved. At least one "Disallow" field must be present in the
robots.txt file.
Robots and the META element
The META element allows HTML authors to tell visiting robots whether a
document may be indexed, or used to harvest more links. No server
administrator action is required.
In the following example a robot should neither index this document,
nor analyze it for links.
<META name="ROBOTS" content="NOINDEX, NOFOLLOW">
The list of terms in the content is ALL, INDEX, NOFOLLOW, NOINDEX.
Note. In early 1997 only a few robots implement this, but this is
expected to change as more public attention is given to controlling
indexing robots.
B.5 Notes on tables
B.5.1 Design rationale
The HTML table model has evolved from studies of existing SGML tables
models, the treatment of tables in common word processing packages,
and a wide range of tabular layout techniques in magazines, books and
other paper-based documents. The model was chosen to allow simple
tables to be expressed simply with extra complexity available when
needed. This makes it practical to create the markup for HTML tables
with everyday text editors and reduces the learning curve for getting
started. This feature has been very important to the success of HTML
to date.
Increasingly, people are creating tables by converting from other
document formats or by creating them directly with WYSIWYG editors. It
is important that the HTML table model fit well with these authoring
tools. This affects how the cells that span multiple rows or columns
are represented, and how alignment and other presentation properties
are associated with groups of cells.
Dynamic reformatting
A major consideration for the HTML table model is that the author does
not control how a user will size a table, what fonts he or she will
use, etc. This makes it risky to rely on column widths specified in
terms of absolute pixel units. Instead, tables must be able to change
sizes dynamically to match the current window size and fonts. Authors
can provide guidance as to the relative widths of columns, but user
agents should ensure that columns are wide enough to render the width
of the largest element of the cell's content. If the author's
specification must be overridden, relative widths of individual
columns should not be changed drastically.
Incremental display
For large tables or slow network connections, incremental table
display is important to user satisfaction. User agents should be able
to begin displaying a table before all of the data has been received.
The default window width for most user agents shows about 80
characters, and the graphics for many HTML pages are designed with
these defaults in mind. By specifying the number of columns, and
including provision for control of table width and the widths of
different columns, authors can give hints to user agents that allow
the incremental display of table contents.
For incremental display, the browser needs the number of columns and
their widths. The default width of the table is the current window
size (width="100%"). This can be altered by setting the width
attribute of the TABLE element. By default, all columns have the same
width, but you can specify column widths with one or more COL elements
before the table data starts.
The remaining issue is the number of columns. Some people have
suggested waiting until the first row of the table has been received,
but this could take a long time if the cells have a lot of content. On
the whole it makes more sense, when incremental display is desired, to
get authors to explicitly specify the number of columns in the TABLE
element.
Authors still need a way of telling user agents whether to use
incremental display or to size the table automatically to fit the cell
contents. In the two pass auto-sizing mode, the number of columns is
determined by the first pass. In the incremental mode, the number of
columns must be stated up front (with COL or COLGROUP elements).
Structure and presentation
HTML distinguishes structural markup such as paragraphs and quotations
from rendering idioms such as margins, fonts, colors, etc. How does
this distinction affect tables? From the purist's point of view, the
alignment of text within table cells and the borders between cells is
a rendering issue, not one of structure. In practice, though, it is
useful to group these with the structural information, as these
features are highly portable from one application to the next. The
HTML table model leaves most rendering information to associated style
sheets. The model presented in this specification is designed to take
advantage of such style sheets but not to require them.
Current desktop publishing packages provide very rich control over the
rendering of tables, and it would be impractical to reproduce this in
HTML, without making HTML into a bulky rich text format like RTF or
MIF. This specification does, however, offer authors the ability to
choose from a set of commonly used classes of border styles. The frame
attribute controls the appearance of the border frame around the table
while the rules attribute determines the choice of rulings within the
table. A finer level of control will be supported via rendering
annotations. The style attribute can be used for specifying rendering
information for individual elements. Further rendering information can
be given with the STYLE element in the document head or via linked
style sheets.
During the development of this specification, a number of avenues were
investigated for specifying the ruling patterns for tables. One issue
concerns the kinds of statements that can be made. Including support
for edge subtraction as well as edge addition leads to relatively
complex algorithms. For instance, work on allowing the full set of
table elements to include the frame and rules attributes led to an
algorithm involving some 24 steps to determine whether a particular
edge of a cell should be ruled or not. Even this additional complexity
doesn't provide enough rendering control to meet the full range of
needs for tables. The current specification deliberately sticks to a
simple intuitive model, sufficient for most purposes. Further
experimental work is needed before a more complex approach is
standardized.
Row and column groups
This specification provides a superset of the simpler model presented
in earlier work on HTML+. Tables are considered as being formed from
an optional caption together with a sequence of rows, which in turn
consist of a sequence of table cells. The model further differentiates
header and data cells, and allows cells to span multiple rows and
columns.
Following the CALS table model (see [CALS]), this specification allows
table rows to be grouped into head and body and foot sections. This
simplifies the representation of rendering information and can be used
to repeat table head and foot rows when breaking tables across page
boundaries, or to provide fixed headers above a scrollable body panel.
In the markup, the foot section is placed before the body sections.
This is an optimization shared with CALS for dealing with very long
tables. It allows the foot to be rendered without having to wait for
the entire table to be processed.
Accessibility
For the visually impaired, HTML offers the hope of setting to rights
the damage caused by the adoption of windows based graphical user
interfaces. The HTML table model includes attributes for labeling each
cell, to support high quality text to speech conversion. The same
attributes can also be used to support automated import and export of
table data to databases or spreadsheets.
B.5.2 Recommended Layout Algorithms
If COL or COLGROUP elements are present, they specify the number of
columns and the table may be rendered using a fixed layout. Otherwise
the autolayout algorithm described below should be used.
If the width attribute is not specified, visual user agents should
assume a default value of 100% for formatting.
It is recommended that user agents increase table widths beyond the
value specified by width in cases when cell contents would otherwise
overflow. User agents that override the specified width should do so
within reason. User agents may elect to split words across lines to
avoid the need for excessive horizontal scrolling or when such
scrolling is impractical or undesired.
For the purposes of layout, user agents should consider that table
captions (specified by the CAPTION element) behave like cells. Each
caption is a cell that spans all of the table's columns if at the top
or bottom of the table, and rows if at the left or right side of the
table.
Fixed Layout Algorithm
For this algorithm, it is assumed that the number of columns is known.
The column widths by default should be set to the same size. Authors
may override this by specifying relative or absolute column widths,
using the COLGROUP or COL elements. The default table width is the
space between the current left and right margins, but may be
overridden by the width attribute on the TABLE element, or determined
from absolute column widths. To deal with mixtures of absolute and
relative column widths, the first step is to allocate space from the
table width to columns with absolute widths. After this, the space
remaining is divided up between the columns with relative widths.
The table syntax alone is insufficient to guarantee the consistency of
attribute values. For instance, the number of COL and COLGROUP
elements may be inconsistent with the number of columns implied by the
table cells. A further problem occurs when the columns are too narrow
to avoid overflow of cell contents. The width of the table as
specified by the TABLE element or COL elements may result in overflow
of cell contents. It is recommended that user agents attempt to
recover gracefully from these situations, e.g., by hyphenating words
and resorting to splitting words if hyphenation points are unknown.
In the event that an indivisible element causes cell overflow, the
user agent may consider adjusting column widths and re-rendering the
table. In the worst case, clipping may be considered if column width
adjustments and/or scrollable cell content are not feasible. In any
case, if cell content is split or clipped this should be indicated to
the user in an appropriate manner.
Autolayout Algorithm
If the number of columns is not specified with COL and COLGROUP
elements, then the user agent should use the following autolayout
algorithm. It uses two passes through the table data and scales
linearly with the size of the table.
In the first pass, line wrapping is disabled, and the user agent keeps
track of the minimum and maximum width of each cell. The maximum width
is given by the widest line. Since line wrap has been disabled,
paragraphs are treated as long lines unless broken by BR elements. The
minimum width is given by the widest text element (word, image, etc.)
taking into account leading indents and list bullets, etc. In other
words, it is necessary to determine the minimum width a cell would
require in a window of its own before the cell begins to overflow.
Allowing user agents to split words will minimize the need for
horizontal scrolling or in the worst case, clipping the cell contents.
This process also applies to any nested tables occurring in cell
content. The minimum and maximum widths for cells in nested tables are
used to determine the minimum and maximum widths for these tables and
hence for the parent table cell itself. The algorithm is linear with
aggregate cell content, and broadly speaking, independent of the depth
of nesting.
To cope with character alignment of cell contents, the algorithm keeps
three running min/max totals for each column: Left of align char,
right of align char and unaligned. The minimum width for a column is
then: max(min_left + min_right, min_non-aligned).
The minimum and maximum cell widths are then used to determine the
corresponding minimum and maximum widths for the columns. These in
turn, are used to find the minimum and maximum width for the table.
Note that cells can contain nested tables, but this doesn't complicate
the code significantly. The next step is to assign column widths
according to the available space (i.e., the space between the current
left and right margins).
For cells that span multiple columns, a simple approach consists of
apportioning the min/max widths evenly to each of the constituent
columns. A slightly more complex approach is to use the min/max widths
of unspanned cells to weight how spanned widths are apportioned.
Experiments suggest that a blend of the two approaches gives good
results for a wide range of tables.
The table borders and intercell margins need to be included in
assigning column widths. There are three cases:
1. The minimum table width is equal to or wider than the available
space. In this case, assign the minimum widths and allow the user
to scroll horizontally. For conversion to braille, it will be
necessary to replace the cells by references to notes containing
their full content. By convention these appear before the table.
2. The maximum table width fits within the available space. In this
case, set the columns to their maximum widths.
3. The maximum width of the table is greater than the available
space, but the minimum table width is smaller. In this case, find
the difference between the available space and the minimum table
width, lets call it W. Lets also call D the difference between
maximum and minimum width of the table.
For each column, let d be the difference between maximum and
minimum width of that column. Now set the column's width to the
minimum width plus d times W over D. This makes columns with large
differences between minimum and maximum widths wider than columns
with smaller differences.
This assignment step is then repeated for nested tables using the
minimum and maximum widths derived for all such tables in the first
pass. In this case, the width of the parent table cell plays the role
of the current window size in the above description. This process is
repeated recursively for all nested tables. The topmost table is then
rendered using the assigned widths. Nested tables are subsequently
rendered as part of the parent table's cell contents.
If the table width is specified with the width attribute, the user
agent attempts to set column widths to match. The width attribute is
not binding if this results in columns having less than their minimum
(i.e., indivisible) widths.
If relative widths are specified with the COL element, the algorithm
is modified to increase column widths over the minimum width to meet
the relative width constraints. The COL elements should be taken as
hints only, so columns shouldn't be set to less than their minimum
width. Similarly, columns shouldn't be made so wide that the table
stretches well beyond the extent of the window. If a COL element
specifies a relative width of zero, the column should always be set to
its minimum width.
When using the two pass layout algorithm, the default alignment
position in the absence of an explicit or inherited charoff attribute
can be determined by choosing the position that would center lines for
which the widths before and after the alignment character are at the
maximum values for any of the lines in the column for which
align="char". For incremental table layout the suggested default is
charoff="50%". If several cells in different rows for the same column
use character alignment, then by default, all such cells should line
up, regardless of which character is used for alignment. Rules for
handling objects too large for a column apply when the explicit or
implied alignment results in a situation where the data exceeds the
assigned width of the column.
Choice of attribute names. It would have been preferable to choose
values for the frame attribute consistent with the rules attribute and
the values used for alignment. For instance: none, top, bottom,
topbot, left, right, leftright, all. Unfortunately, SGML requires
enumerated attribute values to be unique for each element, independent
of the attribute name. This causes immediate problems for "none",
"left", "right" and "all". The values for the frame attribute have
been chosen to avoid clashes with the rules, align, and valign
attributes. This provides a measure of future proofing, as it is
anticipated that the frame and rules attributes will be added to other
table elements in future revisions to this specification. An
alternative would be to make frame a CDATA attribute. The consensus of
the W3C HTML Working Group was that the benefits of being able to use
SGML validation tools to check attributes based on enumerated values
outweighs the need for consistent names.
B.6 Notes on forms
B.6.1 Incremental display
The incremental display of documents being received from the network
gives rise to certain problems with respect to forms. User agents
should prevent forms from being submitted until all of the form's
elements have been received.
The incremental display of documents raises some issues with respect
to tabbing navigation. The heuristic of giving focus to the lowest
valued tabindex in the document seems reasonable enough at first
glance. However this implies having to wait until all of the
document's text is received, since until then, the lowest valued
tabindex may still change. If the user hits the tab key before then,
it is reasonable for user agents to move the focus to the lowest
currently available tabindex.
If forms are associated with client-side scripts, there is further
potential for problems. For instance, a script handler for a given
field may refer to a field that doesn't yet exist.
B.6.2 Future projects
This specification defines a set of elements and attributes powerful
enough to fulfill the general need for producing forms. However there
is still room for many possible improvements. For instance the
following problems could be addressed in the future:
* The range of form field types is too limited in comparison with
modern user interfaces. For instance there is no provision for
tabular data entry, sliders or multiple page layouts.
* Servers cannot update the fields in a submitted form and instead
have to send a complete HTML document causing screen flicker.
* These also cause problems for speech based browsers, making it
difficult for the visually impaired to interact with HTML forms.
Another possible extension would be to add the usemap attribute to
INPUT for use as client-side image map when "type=image". The AREA
element corresponding to the location clicked would contribute the
value to be passed to the server. To avoid the need to modify server
scripts, it may be appropriate to extend AREA to provide x and y
values for use with the INPUT element.
B.7 Notes on scripting
B.7.1 Reserved syntax for future script macros
This specification reserves syntax for the future support of script
macros in HTML CDATA attributes. The intention is to allow attributes
to be set depending on the properties of objects that appear earlier
on the page. The syntax is:
attribute = "... &{ macro body }; ... "
Current Practice for Script Macros
The macro body is made up of one or more statements in the default
scripting language (as per intrinsic event attributes). The semicolon
following the right brace is always needed, as otherwise the right
brace character "}" is treated as being part of the macro body. Its
also worth noting that quote marks are always needed for attributes
containing script macros.
The processing of CDATA attributes proceeds as follows:
1. The SGML parser evaluates any SGML entities (e.g., ">").
2. Next the script macros are evaluated by the script engine.
3. Finally the resultant character string is passed to the
application for subsequent processing.
Macro processing takes place when the document is loaded (or reloaded)
but does not take place again when the document is resized, repainted,
etc.
DEPRECATED EXAMPLE:
Here are some examples using JavaScript. The first one randomizes the
document background color:
<BODY bgcolor='&{randomrgb};'>
Perhaps you want to dim the background for evening viewing:
<BODY bgcolor='&{if(Date.getHours > 18)...};'>
The next example uses JavaScript to set the coordinates for a
client-side image map:
<MAP NAME=foo>
<AREA shape="rect" coords="&{myrect(imageuri)};" href="&{myuri};" alt="">
</MAP>
This example sets the size of an image based upon document properties:
<IMG src="bar.gif" width='&{document.banner.width/2};' height='50%' alt="banner
">
You can set the URI for a link or image by script:
<SCRIPT type="text/javascript">
function manufacturer(widget) {
...
}
function location(manufacturer) {
...
}
function logo(manufacturer) {
...
}
</SCRIPT>
<A href='&{location(manufacturer("widget"))};'>widget</A>
<IMG src='&{logo(manufacturer("widget"))};' alt="logo">
This last example shows how SGML CDATA attributes can be quoted using
single or double quote marks. If you use single quotes around the
attribute string then you can include double quote marks as part of
the attribute string. Another approach is use " for double quote
marks:
<IMG src="&{logo(manufacturer("widget"))};" alt="logo">
B.8 Notes on frames
Since there is no guarantee that a frame target name is unique, it is
appropriate to describe the current practice in finding a frame given
a target name:
1. If the target name is a reserved word as described in the
normative text, apply it as described.
2. Otherwise, perform a depth-first search of the frame hierarchy in
the window that contained the link. Use the first frame whose name
is an exact match.
3. If no such frame was found in (2), apply step 2 to each window, in
a front-to-back ordering. Stop as soon as you encounter a frame
with exactly the same name.
4. If no such frame was found in (3), create a new window and assign
it the target name.
B.9 Notes on accessibility
The W3C Web Accessibility Initiative ([WAI]) is producing a series of
guidelines to improve Web accessibility for people with disabilities.
There are three sets of guidelines:
* Web Content Accessibility Guidelines ([WCGL]), for authors and
site managers. Please consult the Web Content Accessibility
Guidelines for information about supplying alternative text for
images, applets, scripts, etc.
* User Agent Accessibility Guidelines ([UAGL]), for user agent
developers (browsers, multimedia players, assistive technologies).
Please consult these guidelines for guidance on handling alternate
text.
* Authoring Tool Accessibility Guidelines ([ATGL]), for authoring
tool developers.
B.10 Notes on security
Anchors, embedded images, and all other elements that contain URIs as
parameters may cause the URI to be dereferenced in response to user
input. In this case, the security issues of [RFC1738], section 6,
should be considered. The widely deployed methods for submitting form
requests -- HTTP and SMTP -- provide little assurance of
confidentiality. Information providers who request sensitive
information via forms -- especially with the INPUT element,
type="password" -- should be aware and make their users aware of the
lack of confidentiality.
B.10.1 Security issues for forms
A user agent should not send any file that the user has not explicitly
asked to be sent. Thus, HTML user agents are expected to confirm any
default file names that might be suggested by the value attribute of
the INPUT element. Hidden controls must not specify files.
This specification does not contain a mechanism for encryption of the
data; this should be handled by whatever other mechanisms are in place
for secure transmission of data.
Once a file is uploaded, the processing agent should process and store
it appropriately.
References
Contents
1. Normative references
2. Informative references
Normative references
[CSS1]
"Cascading Style Sheets, level 1", H. W. Lie and B. Bos, 17
December 1996. Revised 11 January 1999. This document is
http://www.w3.org/TR/1999/REC-CSS1-19990111
[DATETIME]
"Date and Time Formats", W3C Note, M. Wolf and C. Wicksteed, 15
September 1997. Revised 27 August 1998. This document is
http://www.w3.org/TR/1998/NOTE-datetime-19980827
[HTML40]
"HTML 4.0 Specification", D. Raggett, A. Le Hors, I. Jacobs.
The 24 April 1998 version is
http://www.w3.org/TR/1998/REC-html40-19980424. The 24 April
version included editorial changes from the original 18
December 1997 Revision.
[IANA]
"Assigned Numbers", STD 2, RFC 1700, USC/ISI, J. Reynolds and
J. Postel, October 1994.
[ISO639]
"Codes for the representation of names of languages", ISO
639:1988. For more information, consult
http://www.iso.ch/cate/d4766.html. Refer also to
http://www.oasis-open.org/cover/iso639a.html.
[ISO3166]
"Codes for the representation of names of countries", ISO
3166:1993.
[ISO8601]
"Data elements and interchange formats -- Information
interchange -- Representation of dates and times", ISO
8601:1988.
[ISO8879]
"Information Processing -- Text and Office Systems -- Standard
Generalized Markup Language (SGML)", ISO 8879:1986. Please
consult http://www.iso.ch/cate/d16387.html for information
about the standard.
[ISO10646]
"Information Technology -- Universal Multiple-Octet Coded
Character Set (UCS) -- Part 1: Architecture and Basic
Multilingual Plane", ISO/IEC 10646-1:1993. This reference
refers to a set of codepoints that may evolve as new characters
are assigned to them. This reference therefore includes future
amendments as long as they do not change character assignments
up to and including the first five amendments to ISO/IEC
10646-1:1993. Also, this reference assumes that the character
sets defined by ISO 10646 and Unicode remain
character-by-character equivalent. This reference also includes
future publications of other parts of 10646 (i.e., other than
Part 1) that define characters in planes 1-16.
[ISO88591]
"Information Processing -- 8-bit single-byte coded graphic
character sets -- Part 1: Latin alphabet No. 1", ISO
8859-1:1987.
[MIMETYPES]
List of registered content types (MIME types). Download a list
of registered content types from
ftp://ftp.isi.edu/in-notes/iana/assignments/media-types/.
[RFC1555]
"Hebrew Character Encoding for Internet Messages", H.
Nussbacher and Y. Bourvine, December 1993.
[RFC1556]
"Handling of Bi-directional Texts in MIME", H. Nussbacher,
December 1993.
[RFC1738]
"Uniform Resource Locators", T. Berners-Lee, L. Masinter, and
M. McCahill, December 1994.
[RFC1766]
"Tags for the Identification of Languages", H. Alvestrand,
March 1995. RFC1766 is expected to be updated by
http://www.ietf.org/internet-drafts/draft-alvestrand-lang-tags
-v2-00.txt, currently a work in progress.
[RFC1808]
"Relative Uniform Resource Locators", R. Fielding, June 1995.
[RFC2045]
"Multipurpose Internet Mail Extensions (MIME) Part One: Format
of Internet Message Bodies", N. Freed and N. Borenstein,
November 1996. Note that this RFC obsoletes RFC1521, RFC1522,
and RFC1590.
[RFC2046]
"Multipurpose Internet Mail Extensions (MIME) Part Two: Media
Types", N. Freed and N. Borenstein, November 1996. Note that
this RFC obsoletes RFC1521, RFC1522, and RFC1590.
[RFC2119]
"Key words for use in RFCs to Indicate Requirement Levels", S.
Bradner, March 1997.
[RFC2141]
"URN Syntax", R. Moats, May 1997.
[RFC2279]
"UTF-8, a transformation format of ISO 10646", F. Yergeau,
January 1998. This RFC obsoletes RFC 2044.
[RFC2616]
"Hypertext Transfer Protocol -- HTTP/1.1", R. Fielding, J.
Gettys, J. Mogul, H. Frystyk Nielsen, L. Masinter, P. Leach and
T. Berners-Lee, June 1999. This RFC obsoletes RFC 2068.
[SRGB]
"A Standard Default color Space for the Internet", version
1.10, M. Stokes, M. Anderson, S. Chandrasekar, and R. Motta, 5
November 1996. This document is
http://www.w3.org/Graphics/Color/sRGB
[UNICODE]
The Unicode Consortium. "The Unicode Standard, Version 3.0",
Reading, MA, Addison-Wesley Developers Press, 2000. ISBN
0-201-61633-5. Refer also to
http://www.unicode.org/unicode/standard/versions/.
[URI]
"Uniform Resource Identifiers (URI): Generic Syntax", T.
Berners-Lee, R. Fielding, L. Masinter, August 1998. Note that
RFC 2396 updates [RFC1738] and [RFC1808].
[WEBSGML]
"Final text of revised TC2 to ISO 8879:1986", C. F. Goldfarb,
ed., 6 December 1998.
Informative references
[ATGL]
"Authoring Tool Accessibility Guidelines", J. Treviranus, J.
Richards, I. Jacobs, C. McCathieNevile, eds. The latest Working
Draft of these guidelines for designing accessible authoring
tools is available at http://www.w3.org/TR/WAI-AUTOOLS/
[BRYAN88]
"SGML: An Author's Guide to the Standard Generalized Markup
Language", M. Bryan, Addison-Wesley Publishing Co., 1988.
[CALS]
Continuous Acquisition and Life-Cycle Support (CALS). CALS is a
Department of Defense strategy for achieving effective
creation, exchange, and use of digital data for weapon systems
and equipment. More information can be found on the CALS home
page.
[CHARSETS]
Registered charset values. Download a list of registered
charset values from
ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets.
[CSS2]
"Cascading Style Sheets, level 2", B. Bos, H. W. Lie, C.
Lilley, and I. Jacobs, 12 May 1998. This document is
http://www.w3.org/TR/1998/REC-CSS2-19980512
[DCORE]
The Dublin Core. For more information refer to
http://purl.org/dc
[ETHNO]
"Ethnologue, Languages of the World", 12th Edition, Barbara F.
Grimes editor, Summer Institute of Linguistics, October 1992.
[GOLD90]
"The SGML Handbook", C. F. Goldfarb, Clarendon Press, 1991.
[HTML30]
"HyperText Markup Language Specification Version 3.0", D.
Raggett, September 1995. This document is
http://www.w3.org/MarkUp/html3/CoverPage
[HTML32]
"HTML 3.2 Reference Specification", D. Raggett, 14 January
1997. This document is http://www.w3.org/TR/REC-html32
[HTML3STYLE]
"HTML and Style Sheets", B. Bos, D. Raggett, and H. Lie, 24
March 1997. This document is
http://www.w3.org/TR/WD-style-970324
[LEXHTML]
"A Lexical Analyzer for HTML and Basic SGML", D. Connolly, 15
June 1996. This document is
http://www.w3.org/TR/WD-sgml-lex-960615
[OASISOPEN]
The Organization for the Advancement of Structured Information
Standards (OASIS): http://www.oasis-open.org/.
[PICS]
Platform for Internet Content (PICS). For more information
refer to http://www.w3.org/PICS/
[RDF10]
"Resource Description Framework (RDF) Model and Syntax
Specification", O. Lassila, R. Swick, eds., 22 February 1999.
This document is
http://www.w3.org/TR/1999/REC-rdf-syntax-19990222
[RFC822]
"Standard for the Format of ARPA Internet Text Messages",
Revised by David H. Crocker, August 1982.
[RFC850]
"Standard for Interchange of USENET Messages", M. Horton, June
1983.
[RFC1468]
"Japanese Character Encoding for Internet Messages", J. Murai,
M. Crispin, and E. van der Poel, June 1993.
[RFC1630]
"Universal Resource Identifiers in WWW: A Unifying Syntax for
the Expression of Names and Addresses of Objects on the Network
as used in the World-Wide Web", T. Berners-Lee, June 1994.
[RFC1866]
"HyperText Markup Language 2.0", T. Berners-Lee and D.
Connolly, November 1995.
[RFC1942]
"HTML Tables", Dave Raggett, May 1996.
[RFC2048]
"Multipurpose Internet Mail Extensions (MIME) Part Four:
Registration Procedures", N. Freed, J. Klensin, and J. Postel,
November 1996. Note that this RFC obsoletes RFC1521, RFC1522,
and RFC1590.
[RFC2070]
"Internationalization of the HyperText Markup Language", F.
Yergeau, G. Nicol, G. Adams, and M. Dürst, January 1997.
[RFC2388]
"Returning Values from Forms: multipart/form-data", L.
Masinter, August 1998. Refer also to RFC 1867, "Form-based File
Upload in HTML", E. Nebel and L. Masinter, November 1995.
[SP]
SP is a public domain SGML parser. Further information is
available at http://www.jclark.com/sp/index.htm.
[SQ91]
"The SGML Primer", 3rd Edition, SoftQuad Inc., 1991.
[TAKADA]
"Multilingual Information Exchange through the World-Wide Web",
Toshihiro Takada, Computer Networks and ISDN Systems, Vol. 27,
No. 2, pp. 235-241, November 1994.
[UAGL]
"User Agent Accessibility Guidelines", J. Gunderson and I.
Jacobs, eds. The latest Working Draft of these guidelines for
designing accessible user agents is available at
http://www.w3.org/TR/WAI-USERAGENT.
[WAI]
Guidelines for designing accessible HTML documents are
available at the Web Accessibility Initiative (WAI) Web site:
http://www.w3.org/WAI/.
[WCGL]
"Web Content Accessibility Guidelines 1.0", W. Chisholm, G.
Vanderheiden, and I. Jacobs, eds., 5 May 1999. This document is
http://www.w3.org/TR/1999/WAI-WEBCONTENT-19990505.
[VANH90]
"Practical SGML", E. van Herwijnen, Kluwer Academic Publishers
Group, Norwell and Dordrecht, 1990.
[XHTML]
"XHTML[tm] 1.0: The Extensible HyperText Markup Language", S.
Pemberton et al. The latest version of this specification is
available at http://www.w3.org/TR/xhtml1. As of the publication
of the current document, XHTML 1.0 is a W3C Proposed
Recommendation.
Index of Elements
Legend: Optional, Forbidden, Empty, Deprecated, Loose DTD, Frameset
DTD
Name Start Tag End Tag Empty Depr. DTD Description
A anchor
ABBR abbreviated form (e.g., WWW, HTTP, etc.)
ACRONYM
ADDRESS information on author
APPLET D L Java applet
AREA F E client-side image map area
B bold text style
BASE F E document base URI
BASEFONT F E D L base font size
BDO I18N BiDi over-ride
BIG large text style
BLOCKQUOTE long quotation
BODY O O document body
BR F E forced line break
BUTTON push button
CAPTION table caption
CENTER D L shorthand for DIV align=center
CITE citation
CODE computer code fragment
COL F E table column
COLGROUP O table column group
DD O definition description
DEL deleted text
DFN instance definition
DIR D L directory list
DIV generic language/style container
DL definition list
DT O definition term
EM emphasis
FIELDSET form control group
FONT D L local change to font
FORM interactive form
FRAME F E F subwindow
FRAMESET F window subdivision
H1 heading
H2 heading
H3 heading
H4 heading
H5 heading
H6 heading
HEAD O O document head
HR F E horizontal rule
HTML O O document root element
I italic text style
IFRAME L inline subwindow
IMG F E Embedded image
INPUT F E form control
INS inserted text
ISINDEX F E D L single line prompt
KBD text to be entered by the user
LABEL form field label text
LEGEND fieldset legend
LI O list item
LINK F E a media-independent link
MAP client-side image map
MENU D L menu list
META F E generic metainformation
NOFRAMES F alternate content container for non frame-based
rendering
NOSCRIPT alternate content container for non script-based
rendering
OBJECT generic embedded object
OL ordered list
OPTGROUP option group
OPTION O selectable choice
P O paragraph
PARAM F E named property value
PRE preformatted text
Q short inline quotation
S D L strike-through text style
SAMP sample program output, scripts, etc.
SCRIPT script statements
SELECT option selector
SMALL small text style
SPAN generic language/style container
STRIKE D L strike-through text
STRONG strong emphasis
STYLE style info
SUB subscript
SUP superscript
TABLE
TBODY O O table body
TD O table data cell
TEXTAREA multi-line text field
TFOOT O table footer
TH O table header cell
THEAD O table header
TITLE document title
TR O table row
TT teletype or monospaced text style
U D L underlined text style
UL unordered list
VAR instance of a variable or program argument
Index of Attributes
Legend: Deprecated, Loose DTD, Frameset DTD
Name Related Elements Type Default Depr. DTD Comment
abbr TD, TH %Text; #IMPLIED abbreviation for header cell
accept-charset FORM %Charsets; #IMPLIED list of supported charsets
accept FORM, INPUT %ContentTypes; #IMPLIED list of MIME types for
file upload
accesskey A, AREA, BUTTON, INPUT, LABEL, LEGEND, TEXTAREA %Character;
#IMPLIED accessibility key character
action FORM %URI; #REQUIRED server-side form handler
align CAPTION %CAlign; #IMPLIED D L relative to table
align APPLET, IFRAME, IMG, INPUT, OBJECT %IAlign; #IMPLIED D L
vertical or horizontal alignment
align LEGEND %LAlign; #IMPLIED D L relative to fieldset
align TABLE %TAlign; #IMPLIED D L table position relative to window
align HR (left | center | right) #IMPLIED D L
align DIV, H1, H2, H3, H4, H5, H6, P (left | center | right | justify)
#IMPLIED D L align, text alignment
align COL, COLGROUP, TBODY, TD, TFOOT, TH, THEAD, TR (left | center |
right | justify | char) #IMPLIED
alink BODY %Color; #IMPLIED D L color of selected links
alt APPLET %Text; #IMPLIED D L short description
alt AREA, IMG %Text; #REQUIRED short description
alt INPUT CDATA #IMPLIED short description
archive APPLET CDATA #IMPLIED D L comma-separated archive list
archive OBJECT CDATA #IMPLIED space-separated list of URIs
axis TD, TH CDATA #IMPLIED comma-separated list of related headers
background BODY %URI; #IMPLIED D L texture tile for document
background
bgcolor TABLE %Color; #IMPLIED D L background color for cells
bgcolor TR %Color; #IMPLIED D L background color for row
bgcolor TD, TH %Color; #IMPLIED D L cell background color
bgcolor BODY %Color; #IMPLIED D L document background color
border TABLE %Pixels; #IMPLIED controls frame width around table
border IMG, OBJECT %Pixels; #IMPLIED D L link border width
cellpadding TABLE %Length; #IMPLIED spacing within cells
cellspacing TABLE %Length; #IMPLIED spacing between cells
char COL, COLGROUP, TBODY, TD, TFOOT, TH, THEAD, TR %Character;
#IMPLIED alignment char, e.g. char=':'
charoff COL, COLGROUP, TBODY, TD, TFOOT, TH, THEAD, TR %Length;
#IMPLIED offset for alignment char
charset A, LINK, SCRIPT %Charset; #IMPLIED char encoding of linked
resource
checked INPUT (checked) #IMPLIED for radio buttons and check boxes
cite BLOCKQUOTE, Q %URI; #IMPLIED URI for source document or msg
cite DEL, INS %URI; #IMPLIED info on reason for change
class All elements but BASE, BASEFONT, HEAD, HTML, META, PARAM,
SCRIPT, STYLE, TITLE CDATA #IMPLIED space-separated list of
classes
classid OBJECT %URI; #IMPLIED identifies an implementation
clear BR (left | all | right | none) none D L control of text flow
code APPLET CDATA #IMPLIED D L applet class file
codebase OBJECT %URI; #IMPLIED base URI for classid, data, archive
codebase APPLET %URI; #IMPLIED D L optional base URI for applet
codetype OBJECT %ContentType; #IMPLIED content type for code
color BASEFONT, FONT %Color; #IMPLIED D L text color
cols FRAMESET %MultiLengths; #IMPLIED F list of lengths, default:
100% (1 col)
cols TEXTAREA NUMBER #REQUIRED
colspan TD, TH NUMBER 1 number of cols spanned by cell
compact DIR, DL, MENU, OL, UL (compact) #IMPLIED D L reduced interitem
spacing
content META CDATA #REQUIRED associated information
coords AREA %Coords; #IMPLIED comma-separated list of lengths
coords A %Coords; #IMPLIED for use with client-side image maps
data OBJECT %URI; #IMPLIED reference to object's data
datetime DEL, INS %Datetime; #IMPLIED date and time of change
declare OBJECT (declare) #IMPLIED declare but don't instantiate
flag
defer SCRIPT (defer) #IMPLIED UA may defer execution of script
dir All elements but APPLET, BASE, BASEFONT, BDO, BR, FRAME, FRAMESET,
IFRAME, PARAM, SCRIPT (ltr | rtl) #IMPLIED direction for
weak/neutral text
dir BDO (ltr | rtl) #REQUIRED directionality
disabled BUTTON, INPUT, OPTGROUP, OPTION, SELECT, TEXTAREA (disabled)
#IMPLIED unavailable in this context
enctype FORM %ContentType; "application/x-www- form-urlencoded"
face BASEFONT, FONT CDATA #IMPLIED D L comma-separated list of font
names
for LABEL IDREF #IMPLIED matches field ID value
frame TABLE %TFrame; #IMPLIED which parts of frame to render
frameborder FRAME, IFRAME (1 | 0) 1 F request frame borders?
headers TD, TH IDREFS #IMPLIED list of id's for header cells
height IFRAME %Length; #IMPLIED L frame height
height TD, TH %Length; #IMPLIED D L height for cell
height IMG, OBJECT %Length; #IMPLIED override height
height APPLET %Length; #REQUIRED D L initial height
href A, AREA, LINK %URI; #IMPLIED URI for linked resource
href BASE %URI; #IMPLIED URI that acts as base URI
hreflang A, LINK %LanguageCode; #IMPLIED language code
hspace APPLET, IMG, OBJECT %Pixels; #IMPLIED D L horizontal gutter
http-equiv META NAME #IMPLIED HTTP response header name
id All elements but BASE, HEAD, HTML, META, SCRIPT, STYLE, TITLE ID
#IMPLIED document-wide unique id
ismap IMG, INPUT (ismap) #IMPLIED use server-side image map
label OPTION %Text; #IMPLIED for use in hierarchical menus
label OPTGROUP %Text; #REQUIRED for use in hierarchical menus
lang All elements but APPLET, BASE, BASEFONT, BR, FRAME, FRAMESET,
IFRAME, PARAM, SCRIPT %LanguageCode; #IMPLIED language code
language SCRIPT CDATA #IMPLIED D L predefined script language name
link BODY %Color; #IMPLIED D L color of links
longdesc IMG %URI; #IMPLIED link to long description (complements
alt)
longdesc FRAME, IFRAME %URI; #IMPLIED F link to long description
(complements title)
marginheight FRAME, IFRAME %Pixels; #IMPLIED F margin height in
pixels
marginwidth FRAME, IFRAME %Pixels; #IMPLIED F margin widths in
pixels
maxlength INPUT NUMBER #IMPLIED max chars for text fields
media STYLE %MediaDesc; #IMPLIED designed for use with these media
media LINK %MediaDesc; #IMPLIED for rendering on these media
method FORM (GET | POST) GET HTTP method used to submit the form
multiple SELECT (multiple) #IMPLIED default is single selection
name BUTTON, TEXTAREA CDATA #IMPLIED
name APPLET CDATA #IMPLIED D L allows applets to find each other
name SELECT CDATA #IMPLIED field name
name FORM CDATA #IMPLIED name of form for scripting
name FRAME, IFRAME CDATA #IMPLIED F name of frame for targetting
name IMG CDATA #IMPLIED name of image for scripting
name A CDATA #IMPLIED named link end
name INPUT, OBJECT CDATA #IMPLIED submit as part of form
name MAP CDATA #REQUIRED for reference by usemap
name PARAM CDATA #REQUIRED property name
name META NAME #IMPLIED metainformation name
nohref AREA (nohref) #IMPLIED this region has no action
noresize FRAME (noresize) #IMPLIED F allow users to resize frames?
noshade HR (noshade) #IMPLIED D L
nowrap TD, TH (nowrap) #IMPLIED D L suppress word wrap
object APPLET CDATA #IMPLIED D L serialized applet file
onblur A, AREA, BUTTON, INPUT, LABEL, SELECT, TEXTAREA %Script;
#IMPLIED the element lost the focus
onchange INPUT, SELECT, TEXTAREA %Script; #IMPLIED the element
value was changed
onclick All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT, FRAME,
FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT, STYLE,
TITLE %Script; #IMPLIED a pointer button was clicked
ondblclick All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT,
FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT,
STYLE, TITLE %Script; #IMPLIED a pointer button was double
clicked
onfocus A, AREA, BUTTON, INPUT, LABEL, SELECT, TEXTAREA %Script;
#IMPLIED the element got the focus
onkeydown All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT,
FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT,
STYLE, TITLE %Script; #IMPLIED a key was pressed down
onkeypress All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT,
FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT,
STYLE, TITLE %Script; #IMPLIED a key was pressed and released
onkeyup All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT, FRAME,
FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT, STYLE,
TITLE %Script; #IMPLIED a key was released
onload FRAMESET %Script; #IMPLIED F all the frames have been loaded
onload BODY %Script; #IMPLIED the document has been loaded
onmousedown All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT,
FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT,
STYLE, TITLE %Script; #IMPLIED a pointer button was pressed down
onmousemove All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT,
FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT,
STYLE, TITLE %Script; #IMPLIED a pointer was moved within
onmouseout All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT,
FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT,
STYLE, TITLE %Script; #IMPLIED a pointer was moved away
onmouseover All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT,
FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT,
STYLE, TITLE %Script; #IMPLIED a pointer was moved onto
onmouseup All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT,
FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT,
STYLE, TITLE %Script; #IMPLIED a pointer button was released
onreset FORM %Script; #IMPLIED the form was reset
onselect INPUT, TEXTAREA %Script; #IMPLIED some text was selected
onsubmit FORM %Script; #IMPLIED the form was submitted
onunload FRAMESET %Script; #IMPLIED F all the frames have been
removed
onunload BODY %Script; #IMPLIED the document has been removed
profile HEAD %URI; #IMPLIED named dictionary of meta info
prompt ISINDEX %Text; #IMPLIED D L prompt message
readonly TEXTAREA (readonly) #IMPLIED
readonly INPUT (readonly) #IMPLIED for text and passwd
rel A, LINK %LinkTypes; #IMPLIED forward link types
rev A, LINK %LinkTypes; #IMPLIED reverse link types
rows FRAMESET %MultiLengths; #IMPLIED F list of lengths, default:
100% (1 row)
rows TEXTAREA NUMBER #REQUIRED
rowspan TD, TH NUMBER 1 number of rows spanned by cell
rules TABLE %TRules; #IMPLIED rulings between rows and cols
scheme META CDATA #IMPLIED select form of content
scope TD, TH %Scope; #IMPLIED scope covered by header cells
scrolling FRAME, IFRAME (yes | no | auto) auto F scrollbar or none
selected OPTION (selected) #IMPLIED
shape AREA %Shape; rect controls interpretation of coords
shape A %Shape; rect for use with client-side image maps
size HR %Pixels; #IMPLIED D L
size FONT CDATA #IMPLIED D L [+|-]nn e.g. size="+1", size="4"
size INPUT CDATA #IMPLIED specific to each type of field
size BASEFONT CDATA #REQUIRED D L base font size for FONT elements
size SELECT NUMBER #IMPLIED rows visible
span COL NUMBER 1 COL attributes affect N columns
span COLGROUP NUMBER 1 default number of columns in group
src SCRIPT %URI; #IMPLIED URI for an external script
src INPUT %URI; #IMPLIED for fields with images
src FRAME, IFRAME %URI; #IMPLIED F source of frame content
src IMG %URI; #REQUIRED URI of image to embed
standby OBJECT %Text; #IMPLIED message to show while loading
start OL NUMBER #IMPLIED D L starting sequence number
style All elements but BASE, BASEFONT, HEAD, HTML, META, PARAM,
SCRIPT, STYLE, TITLE %StyleSheet; #IMPLIED associated style info
summary TABLE %Text; #IMPLIED purpose/structure for speech output
tabindex A, AREA, BUTTON, INPUT, OBJECT, SELECT, TEXTAREA NUMBER
#IMPLIED position in tabbing order
target A, AREA, BASE, FORM, LINK %FrameTarget; #IMPLIED L render in
this frame
text BODY %Color; #IMPLIED D L document text color
title All elements but BASE, BASEFONT, HEAD, HTML, META, PARAM,
SCRIPT, TITLE %Text; #IMPLIED advisory title
type A, LINK %ContentType; #IMPLIED advisory content type
type OBJECT %ContentType; #IMPLIED content type for data
type PARAM %ContentType; #IMPLIED content type for value when
valuetype=ref
type SCRIPT %ContentType; #REQUIRED content type of script
language
type STYLE %ContentType; #REQUIRED content type of style language
type INPUT %InputType; TEXT what kind of widget is needed
type LI %LIStyle; #IMPLIED D L list item style
type OL %OLStyle; #IMPLIED D L numbering style
type UL %ULStyle; #IMPLIED D L bullet style
type BUTTON (button | submit | reset) submit for use as form
button
usemap IMG, INPUT, OBJECT %URI; #IMPLIED use client-side image map
valign COL, COLGROUP, TBODY, TD, TFOOT, TH, THEAD, TR (top | middle |
bottom | baseline) #IMPLIED vertical alignment in cells
value INPUT CDATA #IMPLIED Specify for radio buttons and
checkboxes
value OPTION CDATA #IMPLIED defaults to element content
value PARAM CDATA #IMPLIED property value
value BUTTON CDATA #IMPLIED sent to server when submitted
value LI NUMBER #IMPLIED D L reset sequence number
valuetype PARAM (DATA | REF | OBJECT) DATA How to interpret value
version HTML CDATA %HTML.Version; D L Constant
vlink BODY %Color; #IMPLIED D L color of visited links
vspace APPLET, IMG, OBJECT %Pixels; #IMPLIED D L vertical gutter
width HR %Length; #IMPLIED D L
width IFRAME %Length; #IMPLIED L frame width
width IMG, OBJECT %Length; #IMPLIED override width
width TABLE %Length; #IMPLIED table width
width TD, TH %Length; #IMPLIED D L width for cell
width APPLET %Length; #REQUIRED D L initial width
width COL %MultiLength; #IMPLIED column width specification
width COLGROUP %MultiLength; #IMPLIED default width for enclosed
COLs
width PRE NUMBER #IMPLIED D L
Index
A B C D E F G H I L M N O P Q R S T U W
abbreviations and acronyms 1
access key 1
accessibility
access keys 1
alternate object content 1
alternate text 1
and alternate frame content 1
and long frame descriptions 1
and style sheets 1
features in HTML 4 1
long image description 1
of image maps 1, 2
alignment
floating text 1
floats 1
of block-level elements 1
of images 1
of objects 1
of table contents 1
alternate style sheets 1
alternate text
specifying 1
anchor 1
ASCII characters in name 1
case of name 1
character references in name 1
creation of with A 1
creation with id attribute 1
name space of 1
non-ASCII characters in name 1
set by script 1
syntax of name 1
uniqueness of name 1
with A vs. id 1
applet
ways to include 1
application/x-www-form-urlencoded 1, 2
attribute 1
#FIXED value of 1
#IMPLIED value of 1
#REQUIRED value of 1
boolean 1
case of values 1
case-insensitive 1
declaration of in DTD 1
minimized boolean 1
quotation marks around value 1
%attrs; 1
author 1
authoring tool 1, 2
and default style sheet language 1
background color 1
base URI 1
bidirection
Unicode algorithm 1
and character encoding 1
and style sheets 1
override of 1
block-level
and bidirection 1, 2
element 1
%block; 1
BODY
none in frameset 1
boolean attribute 1, 2
minimized 1
border
around a frame 1
around a table 1
around image 1
around object 1
cascading style sheets 1
case
of URIs 1
of anchor name 1
of attribute names 1
of attribute values 1, 2, 3
of character encodings 1
of character entity reference 1
of color names 1
of content types 1
of element names 1
of language codes 1
of length values 1
of link types 1
of media descriptors 1
of numeric character references 1
of script data 1
of style data 1
catalog for HTML 1
CDATA 1, 2
script and style data 1
CERN 1
character encoding 1, 2
UTF-1 1
UTF-16 1
and bidirection 1
choice of 1
common examples 1
default 1
for form submission 1
names of 1
of links 1
specification of 1
user agent's determination of 1
character entity references 1
character reference 1, 2
for directionality 1
character repertoire 1
%Character; 1
characters
abstract 1
access key 1
best effort to render 1
handling undisplayable 1
rendering undisplayable 1
%Charset; 1
checkbox 1
class attribute
roles of 1
client-side image map 1
creation of 1
clipping
table text 1
code position 1
color
background 1
names of 1
%Color; 1
column
number of in a table 1
width of in a table 1
column group 1
comments
character references in 1
in DTD 1
in HTML 1
informative only 1
not rendered 1
used to hide script data 1
used to hide style sheet data 1
conformance 1
content model 1
excluded elements in 1
syntax of in DTD 1
content type
application/x-www-form-urlencoded 1
multipart/form-data 1
text/html 1
content types
for encoding form data 1
Content-Language header 1
Content-Script-Type header 1
Content-Style-Type header 1
Content-Type header 1
%ContentType; 1
control 1
access key for 1
control name 1
control value 1
disabled 1
events for 1
giving focus to 1
initial value 1
read only 1
successful 1
tabbing navigation 1
types of 1
coordinates
of form submit click 1
of server-side image map 1
data cell
in table 1
data type
CDATA 1
ID 1
IDREF 1
IDREFS 1
NAME 1
NUMBER 1
date
format of 1
of inserted and deleted text 1
%Datetime; 1
default
character encoding 1
scripting language 1
style sheet language 1
target frame 1
deprecated 1
elements 1
direction
inheritance of for nested elements 1
of table information 1
of text 1
disabled controls 1
not successful 1
document
SGML validation 1
dynamic modification with script 1
ways to embed 1
ways to include 1, 2
document character set 1
ISO10646 1, 2
equivalence of ISO10646 and UNICODE 1
document type declaration 1
for frameset DTD 1
for strict DTD 1
for transitional DTD 1
document type definition 1
DTD fragments conform to 1
comments in 1
examples conform to 1
frameset 1
how to read 1
strict 1
transitional 1
Dublin Core 1
element
block-level 1
case-insensitive 1
content model of 1
empty 1, 2
end tag 1
inline 1
list of deprecated 1
list of obsolete 1
omitted end tag 1
omitted start tag 1
references from scripts 1
start tag 1
support for deprecated 1
support for obsolete 1
type declaration 1, 2
types 1
unique identifier for 1
empty element 1
end tag 1
declared as optional 1
omitted 1
entity sets
URIs for HTML 4.01 1
error
handling by user agents 1, 2
image map with IMG in BUTTON 1
rendering style rules in STYLE 1
unavailable resource 1
events 1
file select control 1
submission of 1
#FIXED attribute value 1
floating objects 1
floating text 1
focus 1
and access key 1
label gives to control 1
font
style with HTML 1
form
adding labels to 1
content types for encoding 1
control types 1
controls in 1
display notes 1
encoding data of 1
methods and actions 1
navigating through controls 1
processing controls of 1
reset of 1
structuring controls in 1
submission method of 1
submission of 1
tabbing order of controls 1
values submitted 1
form data set 1
encoding 1
fragment identifier 1, 2
frame
URI problems with 1
border of 1
initial contents of 1
inline 1
introduction to 1
list of reserved target names 1
long description of 1
target algorithm 1
target of document 1
white space around 1
frameset
DTD, declaration of 1
DTD, definition of 1
alternate content for 1
navigation problems with 1
nested 1
sharing data among 1
specifying layout of 1
use of NOFRAMES in 1
frameset document 1
%FrameTarget; 1
GET
and form submission 1
header cell
abbreviation 1
in table 1
scope of 1
headings
properly nested 1
hidden control 1, 2
HTML
as SGML application 1
authoring tips 1
comments in 1
development of 1
specifying data external to 1
version 2.0 1
version 3.0 1
version 3.2 1
version HTML+ 1
HTML document 1
HTML Working Group
members of 1
HTTP
Content-Language header 1
Content-Script-Type header 1
Content-Style-Type header 1
Content-Type header 1
Default-Style header 1
GET and POST with forms 1
used to link external style sheets 1
hyphenation 1
ID 1
id attribute
roles of 1
same name space as name attribute 1
IDREF 1
IDREFS 1
image
alignment of 1
border around 1
long description of 1
not directly in frame 1
visual rendering of 1
ways to include 1
white space around 1
width and height of 1
image map 1, 2
accessibility of 1
client-side 1
illegal for IMG in BUTTON 1
overlapping regions of 1
server side 1
server-side 1
with OBJECT 1
#IMPLIED attribute value 1
including an object 1
inline
element 1
%inline; 1
inter-word space 1
Internet Engineering Task Force (IETF) 1
intrinsic events 1
label
and focus 1
explicit association with control 1
implicit association with control 1
lang attribute
not for direction 1
when applicable 1
language
codes to specify 1
of linked resource 1
of script 1
of text 1
%LanguageCode; 1
%Length; 1
line break 1
and bidirectional text 1
and floating text 1
forcing 1
prohibiting 1
link
and character encoding 1
and external style sheets 1, 2
and media-dependent style sheets 1
default target for 1
definition of 1
forward and reverse 1
nesting illegal 1
rendering of 1
semantics with target frame 1
title of 1
type of 1
used to define relationship 1
used to retrieve resource 1
link type
case of 1
list of recognized 1
profiles for new 1
list
definition list 1
nesting of 1
numbering of 1
ordered 1
style sheets and 1
unordered 1
visual rendering of 1
long image description
relation to alt text 1
markup 1
markup language 1
media
and external style sheets 1
used with style sheets 1
media descriptor
case of 1
list of recognized 1
parsing of 1
%MediaDesc; 1
menu 1
grouping of choices 1
preselected options 1
rendering of choices 1
visual rendering of grouped options 1
message entity 1
meta data 1
LINK vs META 1
profiles for 1
scheme for 1
%MultiLength; 1
multipart/form-data 1, 2
NAME 1
notes about minimized 1
NUMBER 1
numbered headings
numbered 1
numeric character reference 1
object
alignment of 1
border around 1
fallback rendering of 1
generic inclusion 1
in HEAD 1, 2, 3
in form 1
initialization 1
locating implementation and data 1
naming schemes for 1
rules for embedded 1
statically declared 1
visual rendering of 1
white space around 1
width and height of 1
object control 1, 2
obsolete 1
elements 1
paragraph
visual rendering of 1
parameter entity
%Character; 1
%Charset; 1
%Color; 1
%ContentType; 1
%Datetime; 1
%FrameTarget; 1
%LanguageCode; 1
%Length; 1
%MediaDesc; 1
%MultiLength; 1
%Pixels; 1
%Script; 1
%Text; 1
%URI; 1
%attrs; 1
%block; 1
%inline; 1
parameter entity definition 1
password input control 1
persistent style sheets 1
pixel 1
%Pixels; 1
Platform for Internet Content Selection (PICS) 1
POST
and form submission 1
for non-ASCII form data 1
preferred style sheets 1
profile 1
push button 1
quoted text 1
rendering of 1
radio button 1
read only controls 1
relative length 1
relative URI 1
resolution of 1
#REQUIRED attribute value 1
reset button 1
resetting a form 1
resolution of relative URI 1
Resource Description Framework (RDF) 1, 2
row
number of in table 1
row group 1
rule
between block-level elements 1
between table cells 1
scheme 1
scope
of table header cell 1
script
comments to hide 1
data 1
executed on event 1
executed when document loaded 1
implementation notes 1
introduction to 1
references to elements 1
reserved syntax for 1
used to modify document 1
used to set anchor 1
uses of 1
when unsupported 1
%Script; 1
scripting language
default 1
local declaration 1
specification of 1
search engine
and links 1
helping 1, 2
search robot
helping 1
security
notes on 1
of password control 1
server-side image map 1, 2
click coordinates 1
SGML
application 1
catalog for HTML 1
declaration 1
declaration of HTML 4 1
document character set 1
document type definition (DTD) 1
document validation 1
element type declaration 1
features with limited support 1, 2
implementation notes 1
introduction to 1
treatment of line breaks 1
soft hyphen 1
start tag 1
omitted 1
strict DTD
declaration of 1
definition of 1
style sheet
alternate 1
and bidirection 1
cascading 1
comments to hide 1
data 1
external 1
external through links 1
inline rules 1
introduction to 1
persistent 1
preferred 1
rules in HEAD 1
specification of external 1
specification of preferred 1
target media for 1
used with DIV and SPAN 1
style sheet language
default 1
submit button 1
successful control 1
summary
of table contents 1
tabbing navigation 1
tabbing order 1
table
algorithm to find heading 1
alignment of contents 1
borders and rules of 1
caption for 1
categorization of cells 1
cell margins 1
cells that span several rows/columns 1
column group in 1
data cells 1
directionality of 1
header cells 1
incremental display notes 1
incremental rendering of 1
layout algorithms for 1
non-visual rendering of 1
not for formatting pages 1
number of columns 1
number of rows 1
row group in 1
speaking cell data 1
summary of contents 1
visual rendering of 1
width of columns 1
target frame
algorithm 1
default 1
reserved names 1
semantics of 1
specification of 1
text
direction of 1
floating 1
markup for inserted and deleted 1
preformatted 1
quoted 1
wrapping in paragraph 1
text input control 1
multi-line 1
single-line 1
text/html 1
%Text; 1
time
format of 1
title
available to user 1
of a document 1
used to annotate elements 1
transitional DTD
declaration of 1
definition of 1
Unicode bidirectional algorithm 1
universal character set 1
Universal Resource Identifier (see URI) 1
URI
case of 1
non-ASCII characters in attribute values 1
relative 1
resolution of relative 1, 2
specifying base 1
uses of in HTML 1
%URI; 1
URL
relationship to URI 1
user 1
user agent 1
and error conditions 1, 2
and script data 1
and style data 1
conforming 1
handling image maps 1
processing script and style data 1
UTF-1 1
UTF-16 1
white space 1
around frame 1
around images and objects 1
around table contents 1
character 1
collapsed 1
preserved in PRE 1
World Wide Web (Web) 1
wrapping text 1