Web Content Accessibility Guidelines 1.0
W3C Recommendation
This version:
http://www.w3.org/TR/1999/WAI-WEBCONTENT-19990505
(plain text, PostScript, PDF, gzip tar file of HTML, zip
archive of HTML)
Latest version:
http://www.w3.org/TR/WAI-WEBCONTENT
Previous version:
http://www.w3.org/TR/1999/WAI-WEBCONTENT-19990324
Abstract
These guidelines explain how to make Web content accessible to people
with disabilities. The guidelines are intended for all Web content
developers (page authors and site designers) and for developers of
authoring tools. The primary goal of these guidelines is to promote
accessibility. However, following them will also make Web content more
available to all users, whatever user agent they are using (e.g.,
desktop browser, voice browser, mobile phone, automobile-based
personal computer, etc.) or constraints they may be operating under
(e.g., noisy surroundings, under- or over-illuminated rooms, in a
hands-free environment, etc.). Following these guidelines will also
help people find information on the Web more quickly. These guidelines
do not discourage content developers from using images, video, etc.,
but rather explain how to make multimedia content more accessible to a
wide audience.
This is a reference document for accessibility principles and design
ideas. Some of the strategies discussed in this document address
certain Web internationalization and mobile access concerns. However,
this document focuses on accessibility and does not fully address the
related concerns of other W3C Activities. Please consult the W3C
Mobile Access Activity home page and the W3C Internationalization
Activity home page for more information.
This document is meant to be stable and therefore does not provide
specific information about browser support for different technologies
as that information changes rapidly. Instead, the Web Accessibility
Initiative (WAI) Web site provides such information (refer to
[WAI-UA-SUPPORT]).
This document includes an appendix that organizes all of the
checkpoints by topic and priority. The checkpoints in the appendix
link to their definitions in the current document. The topics
identified in the appendix include images, multimedia, tables, frames,
forms, and scripts. The appendix is available as either a tabular
summary of checkpoints or as a simple list of checkpoints.
A separate document, entitled "Techniques for Web Content
Accessibility Guidelines 1.0" ([TECHNIQUES]), explains how to
implement the checkpoints defined in the current document. The
Techniques Document discusses each checkpoint in more detail and
provides examples using the Hypertext Markup Language (HTML),
Cascading Style Sheets (CSS), Synchronized Multimedia Integration
Language (SMIL), and the Mathematical Markup Language (MathML). The
Techniques Document also includes techniques for document validation
and testing, and an index of HTML elements and attributes (and which
techniques use them). The Techniques Document has been designed to
track changes in technology and is expected to be updated more
frequently than the current document. Note. Not all browsers or
multimedia tools may support the features described in the guidelines.
In particular, new features of HTML 4.0 or CSS 1 or CSS 2 may not be
supported.
"Web Content Accessibility Guidelines 1.0" is part of a series of
accessibility guidelines published by the Web Accessibility
Initiative. The series also includes User Agent Accessibility
Guidelines ([WAI-USERAGENT]) and Authoring Tool Accessibility
Guidelines ([WAI-AUTOOLS]).
Status of this document
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 documents. 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
universality of the Web.
The English version of this specification is the only normative
version. However, for translations in other languages see
http://www.w3.org/WAI/GL/WAI-WEBCONTENT-TRANSLATIONS.
The list of known errors in this document is available at
http://www.w3.org/WAI/GL/WAI-WEBCONTENT-ERRATA. Please report errors
in this document to wai-wcag-editor@w3.org.
A list of current W3C Recommendations and other technical documents
can be found at http://www.w3.org/TR.
This document has been produced as part of the W3C Web Accessibility
Initiative. The goal of the Web Content Guidelines Working Group is
discussed in the Working Group charter.
Table of Contents
* Abstract
* Status of this document
* 1. Introduction
* 2. Themes of Accessible Design
+ 2.1 Ensuring Graceful Transformation
+ 2.2 Making Content Understandable and Navigable
* 3. How the Guidelines are Organized
+ 3.1 Document conventions
* 4. Priorities
* 5. Conformance
* 6. Web Content Accessibility Guidelines
+ 1. Provide equivalent alternatives to auditory and visual
content.
+ 2. Don't rely on color alone.
+ 3. Use markup and style sheets and do so properly.
+ 4. Clarify natural language usage
+ 5. Create tables that transform gracefully.
+ 6. Ensure that pages featuring new technologies transform
gracefully.
+ 7. Ensure user control of time-sensitive content changes.
+ 8. Ensure direct accessibility of embedded user interfaces.
+ 9. Design for device-independence.
+ 10. Use interim solutions.
+ 11. Use W3C technologies and guidelines.
+ 12. Provide context and orientation information.
+ 13. Provide clear navigation mechanisms.
+ 14. Ensure that documents are clear and simple.
* Appendix A. -- Validation
* Appendix B. -- Glossary
* Acknowledgments
* References
The appendix list of checkpoints is available as either a tabular
summary of checkpoints or as a simple list of checkpoints.
1. Introduction
For those unfamiliar with accessibility issues pertaining to Web page
design, consider that many users may be operating in contexts very
different from your own:
* They may not be able to see, hear, move, or may not be able to
process some types of information easily or at all.
* They may have difficulty reading or comprehending text.
* They may not have or be able to use a keyboard or mouse.
* They may have a text-only screen, a small screen, or a slow
Internet connection.
* They may not speak or understand fluently the language in which
the document is written.
* They may be in a situation where their eyes, ears, or hands are
busy or interfered with (e.g., driving to work, working in a loud
environment, etc.).
* They may have an early version of a browser, a different browser
entirely, a voice browser, or a different operating system.
Content developers must consider these different situations during
page design. While there are several situations to consider, each
accessible design choice generally benefits several disability groups
at once and the Web community as a whole. For example, by using style
sheets to control font styles and eliminating the FONT element, HTML
authors will have more control over their pages, make those pages more
accessible to people with low vision, and by sharing the style sheets,
will often shorten page download times for all users.
The guidelines discuss accessibility issues and provide accessible
design solutions. They address typical scenarios (similar to the font
style example) that may pose problems for users with certain
disabilities. For example, the first guideline explains how content
developers can make images accessible. Some users may not be able to
see images, others may use text-based browsers that do not support
images, while others may have turned off support for images (e.g., due
to a slow Internet connection). The guidelines do not suggest avoiding
images as a way to improve accessibility. Instead, they explain that
providing a text equivalent of the image will make it accessible.
How does a text equivalent make the image accessible? Both words in
"text equivalent" are important:
* Text content can be presented to the user as synthesized speech,
braille, and visually-displayed text. Each of these three
mechanisms uses a different sense -- ears for synthesized speech,
tactile for braille, and eyes for visually-displayed text --
making the information accessible to groups representing a variety
of sensory and other disabilities.
* In order to be useful, the text must convey the same function or
purpose as the image. For example, consider a text equivalent for
a photographic image of the Earth as seen from outer space. If the
purpose of the image is mostly that of decoration, then the text
"Photograph of the Earth as seen from outer space" might fulfill
the necessary function. If the purpose of the photograph is to
illustrate specific information about world geography, then the
text equivalent should convey that information. If the photograph
has been designed to tell the user to select the image (e.g., by
clicking on it) for information about the earth, equivalent text
would be "Information about the Earth". Thus, if the text conveys
the same function or purpose for the user with a disability as the
image does for other users, then it can be considered a text
equivalent.
Note that, in addition to benefitting users with disabilities, text
equivalents can help all users find pages more quickly, since search
robots can use the text when indexing the pages.
While Web content developers must provide text equivalents for images
and other multimedia content, it is the responsibility of user agents
(e.g., browsers and assistive technologies such as screen readers,
braille displays, etc.) to present the information to the user.
Non-text equivalents of text (e.g., icons, pre-recorded speech, or a
video of a person translating the text into sign language) can make
documents accessible to people who may have difficulty accessing
written text, including many individuals with cognitive disabilities,
learning disabilities, and deafness. Non-text equivalents of text can
also be helpful to non-readers. An auditory description is an example
of a non-text equivalent of visual information. An auditory
description of a multimedia presentation's visual track benefits
people who cannot see the visual information.
2. Themes of Accessible Design
The guidelines address two general themes: ensuring graceful
transformation, and making content understandable and navigable.
2.1 Ensuring Graceful Transformation
By following these guidelines, content developers can create pages
that transform gracefully. Pages that transform gracefully remain
accessible despite any of the constraints described in the
introduction, including physical, sensory, and cognitive
disabilities, work constraints, and technological barriers. Here are
some keys to designing pages that transform gracefully:
* Separate structure from presentation (refer to the difference
between content, structure, and presentation).
* Provide text (including text equivalents). Text can be rendered in
ways that are available to almost all browsing devices and
accessible to almost all users.
* Create documents that work even if the user cannot see and/or
hear. Provide information that serves the same purpose or function
as audio or video in ways suited to alternate sensory channels as
well. This does not mean creating a prerecorded audio version of
an entire site to make it accessible to users who are blind. Users
who are blind can use screen reader technology to render all text
information in a page.
* Create documents that do not rely on one type of hardware. Pages
should be usable by people without mice, with small screens, low
resolution screens, black and white screens, no screens, with only
voice or text output, etc.
The theme of graceful transformation is addressed primarily by
guidelines 1 to 11.
2.2 Making Content Understandable and Navigable
Content developers should make content understandable and navigable.
This includes not only making the language clear and simple, but also
providing understandable mechanisms for navigating within and between
pages. Providing navigation tools and orientation information in pages
will maximize accessibility and usability. Not all users can make use
of visual clues such as image maps, proportional scroll bars,
side-by-side frames, or graphics that guide sighted users of graphical
desktop browsers. Users also lose contextual information when they can
only view a portion of a page, either because they are accessing the
page one word at a time (speech synthesis or braille display), or one
section at a time (small display, or a magnified display). Without
orientation information, users may not be able to understand very
large tables, lists, menus, etc.
The theme of making content understandable and navigable is addressed
primarily in guidelines 12 to 14.
3. How the Guidelines are Organized
This document includes fourteen guidelines, or general principles of
accessible design. Each guideline includes:
* The guideline number.
* The statement of the guideline.
* Guideline navigation links. Three links allow navigation to the
next guideline (right arrow icon), the previous guideline (left
arrow icon), or the current guideline's position in the table of
contents (up arrow icon).
* The rationale behind the guideline and some groups of users who
benefit from it.
* A list of checkpoint definitions.
The checkpoint definitions in each guideline explain how the guideline
applies in typical content development scenarios. Each checkpoint
definition includes:
* The checkpoint number.
* The statement of the checkpoint.
* The priority of the checkpoint. Priority 1 checkpoints are
highlighted through the use of style sheets.
* Optional informative notes, clarifying examples, and cross
references to related guidelines or checkpoints.
* A link to a section of the Techniques Document ([TECHNIQUES])
where implementations and examples of the checkpoint are
discussed.
Each checkpoint is intended to be specific enough so that someone
reviewing a page or site may verify that the checkpoint has been
satisfied.
3.1 Document conventions
The following editorial conventions are used throughout this document:
* Element names are in uppercase letters.
* Attribute names are quoted in lowercase letters.
* Links to definitions are highlighted through the use of style
sheets.
4. Priorities
Each checkpoint has a priority level assigned by the Working Group
based on the checkpoint's impact on accessibility.
[Priority 1]
A Web content developer must satisfy this checkpoint.
Otherwise, one or more groups will find it impossible to access
information in the document. Satisfying this checkpoint is a
basic requirement for some groups to be able to use Web
documents.
[Priority 2]
A Web content developer should satisfy this checkpoint.
Otherwise, one or more groups will find it difficult to access
information in the document. Satisfying this checkpoint will
remove significant barriers to accessing Web documents.
[Priority 3]
A Web content developer may address this checkpoint. Otherwise,
one or more groups will find it somewhat difficult to access
information in the document. Satisfying this checkpoint will
improve access to Web documents.
Some checkpoints specify a priority level that may change under
certain (indicated) conditions.
5. Conformance
This section defines three levels of conformance to this document:
* Conformance Level "A": all Priority 1 checkpoints are satisfied;
* Conformance Level "Double-A": all Priority 1 and 2 checkpoints are
satisfied;
* Conformance Level "Triple-A": all Priority 1, 2, and 3 checkpoints
are satisfied;
Note. Conformance levels are spelled out in text so they may be
understood when rendered to speech.
Claims of conformance to this document must use one of the following
two forms.
Form 1: Specify:
* The guidelines title: "Web Content Accessibility Guidelines 1.0"
* The guidelines URI:
http://www.w3.org/TR/1999/WAI-WEBCONTENT-19990505
* The conformance level satisfied: "A", "Double-A", or "Triple-A".
* The scope covered by the claim (e.g., page, site, or defined
portion of a site.).
Example of Form 1:
This page conforms to W3C's "Web Content Accessibility Guidelines
1.0", available at
http://www.w3.org/TR/1999/WAI-WEBCONTENT-19990505, level Double-A.
Form 2: Include, on each page claiming conformance, one of three icons
provided by W3C and link the icon to the appropriate W3C explanation
of the claim. Information about the icons and how to insert them in
pages is available at [WCAG-ICONS].
6. Web Content Accessibility Guidelines
Guideline 1. Provide equivalent alternatives to auditory and visual content.
Next guideline: 2 Previous guideline: 14 Go to contents
Provide content that, when presented to the user, conveys essentially the
same function or purpose as auditory or visual content.
Although some people cannot use images, movies, sounds, applets, etc.
directly, they may still use pages that include equivalent information
to the visual or auditory content. The equivalent information must
serve the same purpose as the visual or auditory content. Thus, a text
equivalent for an image of an upward arrow that links to a table of
contents could be "Go to table of contents". In some cases, an
equivalent should also describe the appearance of visual content
(e.g., for complex charts, billboards, or diagrams) or the sound of
auditory content (e.g., for audio samples used in education).
This guideline emphasizes the importance of providing text equivalents
of non-text content (images, pre-recorded audio, video). The power of
text equivalents lies in their capacity to be rendered in ways that
are accessible to people from various disability groups using a
variety of technologies. Text can be readily output to speech
synthesizers and braille displays, and can be presented visually (in a
variety of sizes) on computer displays and paper. Synthesized speech
is critical for individuals who are blind and for many people with the
reading difficulties that often accompany cognitive disabilities,
learning disabilities, and deafness. Braille is essential for
individuals who are both deaf and blind, as well as many individuals
whose only sensory disability is blindness. Text displayed visually
benefits users who are deaf as well as the majority of Web users.
Providing non-text equivalents (e.g., pictures, videos, and
pre-recorded audio) of text is also beneficial to some users,
especially nonreaders or people who have difficulty reading. In movies
or visual presentations, visual action such as body language or other
visual cues may not be accompanied by enough audio information to
convey the same information. Unless verbal descriptions of this visual
information are provided, people who cannot see (or look at) the
visual content will not be able to perceive it.
Checkpoints:
1.1 Provide a text equivalent for every non-text element (e.g., via
"alt", "longdesc", or in element content). This includes:
images, graphical representations of text (including symbols),
image map regions, animations (e.g., animated GIFs), applets
and programmatic objects, ascii art, frames, scripts, images
used as list bullets, spacers, graphical buttons, sounds
(played with or without user interaction), stand-alone audio
files, audio tracks of video, and video. [Priority 1]
For example, in HTML:
+ Use "alt" for the IMG, INPUT, and APPLET elements, or provide
a text equivalent in the content of the OBJECT and APPLET
elements.
+ For complex content (e.g., a chart) where the "alt" text does
not provide a complete text equivalent, provide an additional
description using, for example, "longdesc" with IMG or FRAME,
a link inside an OBJECT element, or a description link.
+ For image maps, either use the "alt" attribute with AREA, or
use the MAP element with A elements (and other text) as
content.
Refer also to checkpoint 9.1 and checkpoint 13.10.
Techniques for checkpoint 1.1
1.2 Provide redundant text links for each active region of a
server-side image map. [Priority 1]
Refer also to checkpoint 1.5 and checkpoint 9.1.
Techniques for checkpoint 1.2
1.3 Until user agents can automatically read aloud the text equivalent
of a visual track, provide an auditory description of the
important information of the visual track of a multimedia
presentation. [Priority 1]
Synchronize the auditory description with the audio track as
per checkpoint 1.4. Refer to checkpoint 1.1 for information
about textual equivalents for visual information.
Techniques for checkpoint 1.3
1.4 For any time-based multimedia presentation (e.g., a movie or
animation), synchronize equivalent alternatives (e.g., captions
or auditory descriptions of the visual track) with the
presentation. [Priority 1]
Techniques for checkpoint 1.4
1.5 Until user agents render text equivalents for client-side image
map links, provide redundant text links for each active region
of a client-side image map. [Priority 3]
Refer also to checkpoint 1.2 and checkpoint 9.1.
Techniques for checkpoint 1.5
Guideline 2. Don't rely on color alone.
Next guideline: 3 Previous guideline: 1 Go to contents
Ensure that text and graphics are understandable when viewed without color.
If color alone is used to convey information, people who cannot
differentiate between certain colors and users with devices that have
non-color or non-visual displays will not receive the information.
When foreground and background colors are too close to the same hue,
they may not provide sufficient contrast when viewed using monochrome
displays or by people with different types of color deficits.
Checkpoints:
2.1 Ensure that all information conveyed with color is also available
without color, for example from context or markup. [Priority 1]
Techniques for checkpoint 2.1
2.2 Ensure that foreground and background color combinations provide
sufficient contrast when viewed by someone having color
deficits or when viewed on a black and white screen.
[Priority 2 for images, Priority 3 for text].
Techniques for checkpoint 2.2
Guideline 3. Use markup and style sheets and do so properly.
Next guideline: 4 Previous guideline: 2 Go to contents
Mark up documents with the proper structural elements. Control presentation
with style sheets rather than with presentation elements and attributes.
Using markup improperly -- not according to specification -- hinders
accessibility. Misusing markup for a presentation effect (e.g., using
a table for layout or a header to change the font size) makes it
difficult for users with specialized software to understand the
organization of the page or to navigate through it. Furthermore, using
presentation markup rather than structural markup to convey structure
(e.g., constructing what looks like a table of data with an HTML PRE
element) makes it difficult to render a page intelligibly to other
devices (refer to the description of difference between content,
structure, and presentation).
Content developers may be tempted to use (or misuse) constructs that
achieve a desired formatting effect on older browsers. They must be
aware that these practices cause accessibility problems and must
consider whether the formatting effect is so critical as to warrant
making the document inaccessible to some users.
At the other extreme, content developers must not sacrifice
appropriate markup because a certain browser or assistive technology
does not process it correctly. For example, it is appropriate to use
the TABLE element in HTML to mark up tabular information even though
some older screen readers may not handle side-by-side text correctly
(refer to checkpoint 10.3). Using TABLE correctly and creating tables
that transform gracefully (refer to guideline 5) makes it possible for
software to render tables other than as two-dimensional grids.
Checkpoints:
3.1 When an appropriate markup language exists, use markup rather than
images to convey information. [Priority 2]
For example, use MathML to mark up mathematical equations, and
style sheets to format text and control layout. Also, avoid
using images to represent text -- use text and style sheets
instead. Refer also to guideline 6 and guideline 11.
Techniques for checkpoint 3.1
3.2 Create documents that validate to published formal grammars.
[Priority 2]
For example, include a document type declaration at the
beginning of a document that refers to a published DTD (e.g.,
the strict HTML 4.0 DTD).
Techniques for checkpoint 3.2
3.3 Use style sheets to control layout and presentation. [Priority 2]
For example, use the CSS 'font' property instead of the HTML
FONT element to control font styles.
Techniques for checkpoint 3.3
3.4 Use relative rather than absolute units in markup language
attribute values and style sheet property values. [Priority 2]
For example, in CSS, use 'em' or percentage lengths rather than
'pt' or 'cm', which are absolute units. If absolute units are
used, validate that the rendered content is usable (refer to
the section on validation).
Techniques for checkpoint 3.4
3.5 Use header elements to convey document structure and use them
according to specification. [Priority 2]
For example, in HTML, use H2 to indicate a subsection of H1. Do
not use headers for font effects.
Techniques for checkpoint 3.5
3.6 Mark up lists and list items properly. [Priority 2]
For example, in HTML, nest OL, UL, and DL lists properly.
Techniques for checkpoint 3.6
3.7 Mark up quotations. Do not use quotation markup for formatting
effects such as indentation. [Priority 2]
For example, in HTML, use the Q and BLOCKQUOTE elements to
markup short and longer quotations, respectively.
Techniques for checkpoint 3.7
Guideline 4. Clarify natural language usage
Next guideline: 5 Previous guideline: 3 Go to contents
Use markup that facilitates pronunciation or interpretation of abbreviated
or foreign text.
When content developers mark up natural language changes in a
document, speech synthesizers and braille devices can automatically
switch to the new language, making the document more accessible to
multilingual users. Content developers should identify the predominant
natural language of a document's content (through markup or HTTP
headers). Content developers should also provide expansions of
abbreviations and acronyms.
In addition to helping assistive technologies, natural language markup
allows search engines to find key words and identify documents in a
desired language. Natural language markup also improves readability of
the Web for all people, including those with learning disabilities,
cognitive disabilities, or people who are deaf.
When abbreviations and natural language changes are not identified,
they may be indecipherable when machine-spoken or brailled.
Checkpoints:
4.1 Clearly identify changes in the natural language of a document's
text and any text equivalents (e.g., captions). [Priority 1]
For example, in HTML use the "lang" attribute. In XML, use
"xml:lang".
Techniques for checkpoint 4.1
4.2 Specify the expansion of each abbreviation or acronym in a
document where it first occurs. [Priority 3]
For example, in HTML, use the "title" attribute of the ABBR and
ACRONYM elements. Providing the expansion in the main body of
the document also helps document usability.
Techniques for checkpoint 4.2
4.3 Identify the primary natural language of a document. [Priority 3]
For example, in HTML set the "lang" attribute on the HTML
element. In XML, use "xml:lang". Server operators should
configure servers to take advantage of HTTP content negotiation
mechanisms ([RFC2068], section 14.13) so that clients can
automatically retrieve documents of the preferred language.
Techniques for checkpoint 4.3
Guideline 5. Create tables that transform gracefully.
Next guideline: 6 Previous guideline: 4 Go to contents
Ensure that tables have necessary markup to be transformed by accessible
browsers and other user agents.
Tables should be used to mark up truly tabular information ("data
tables"). Content developers should avoid using them to lay out pages
("layout tables"). Tables for any use also present special problems to
users of screen readers (refer to checkpoint 10.3).
Some user agents allow users to navigate among table cells and access
header and other table cell information. Unless marked-up properly,
these tables will not provide user agents with the appropriate
information. (Refer also to guideline 3.)
The following checkpoints will directly benefit people who access a
table through auditory means (e.g., a screen reader or an
automobile-based personal computer) or who view only a portion of the
page at a time (e.g., users with blindness or low vision using speech
output or a braille display, or other users of devices with small
displays, etc.).
Checkpoints:
5.1 For data tables, identify row and column headers. [Priority 1]
For example, in HTML, use TD to identify data cells and TH to
identify headers.
Techniques for checkpoint 5.1
5.2 For data tables that have two or more logical levels of row or
column headers, use markup to associate data cells and header
cells. [Priority 1]
For example, in HTML, use THEAD, TFOOT, and TBODY to group
rows, COL and COLGROUP to group columns, and the "axis",
"scope", and "headers" attributes, to describe more complex
relationships among data.
Techniques for checkpoint 5.2
5.3 Do not use tables for layout unless the table makes sense when
linearized. Otherwise, if the table does not make sense,
provide an alternative equivalent (which may be a linearized
version). [Priority 2]
Note. Once user agents support style sheet positioning, tables
should not be used for layout. Refer also to checkpoint 3.3.
Techniques for checkpoint 5.3
5.4 If a table is used for layout, do not use any structural markup
for the purpose of visual formatting. [Priority 2]
For example, in HTML do not use the TH element to cause the
content of a (non-table header) cell to be displayed centered
and in bold.
Techniques for checkpoint 5.4
5.5 Provide summaries for tables. [Priority 3]
For example, in HTML, use the "summary" attribute of the TABLE
element.
Techniques for checkpoint 5.5
5.6 Provide abbreviations for header labels. [Priority 3]
For example, in HTML, use the "abbr" attribute on the TH
element.
Techniques for checkpoint 5.6
Refer also to checkpoint 10.3.
Guideline 6. Ensure that pages featuring new technologies transform
gracefully.
Next guideline: 7 Previous guideline: 5 Go to contents
Ensure that pages are accessible even when newer technologies are not
supported or are turned off.
Although content developers are encouraged to use new technologies
that solve problems raised by existing technologies, they should know
how to make their pages still work with older browsers and people who
choose to turn off features.
Checkpoints:
6.1 Organize documents so they may be read without style sheets. For
example, when an HTML document is rendered without associated
style sheets, it must still be possible to read the document.
[Priority 1]
When content is organized logically, it will be rendered in a
meaningful order when style sheets are turned off or not
supported.
Techniques for checkpoint 6.1
6.2 Ensure that equivalents for dynamic content are updated when the
dynamic content changes. [Priority 1]
Techniques for checkpoint 6.2
6.3 Ensure that pages are usable when scripts, applets, or other
programmatic objects are turned off or not supported. If this
is not possible, provide equivalent information on an
alternative accessible page. [Priority 1]
For example, ensure that links that trigger scripts work when
scripts are turned off or not supported (e.g., do not use
"javascript:" as the link target). If it is not possible to
make the page usable without scripts, provide a text equivalent
with the NOSCRIPT element, or use a server-side script instead
of a client-side script, or provide an alternative accessible
page as per checkpoint 11.4. Refer also to guideline 1.
Techniques for checkpoint 6.3
6.4 For scripts and applets, ensure that event handlers are input
device-independent. [Priority 2]
Refer to the definition of device independence.
Techniques for checkpoint 6.4
6.5 Ensure that dynamic content is accessible or provide an
alternative presentation or page. [Priority 2]
For example, in HTML, use NOFRAMES at the end of each frameset.
For some applications, server-side scripts may be more
accessible than client-side scripts.
Techniques for checkpoint 6.5
Refer also to checkpoint 11.4.
Guideline 7. Ensure user control of time-sensitive content changes.
Next guideline: 8 Previous guideline: 6 Go to contents
Ensure that moving, blinking, scrolling, or auto-updating objects or pages
may be paused or stopped.
Some people with cognitive or visual disabilities are unable to read
moving text quickly enough or at all. Movement can also cause such a
distraction that the rest of the page becomes unreadable for people
with cognitive disabilities. Screen readers are unable to read moving
text. People with physical disabilities might not be able to move
quickly or accurately enough to interact with moving objects.
Note. All of the following checkpoints involve some content developer
responsibility until user agents provide adequate feature control
mechanisms.
Checkpoints:
7.1 Until user agents allow users to control flickering, avoid causing
the screen to flicker. [Priority 1]
Note. People with photosensitive epilepsy can have seizures
triggered by flickering or flashing in the 4 to 59 flashes per
second (Hertz) range with a peak sensitivity at 20 flashes per
second as well as quick changes from dark to light (like strobe
lights).
Techniques for checkpoint 7.1
7.2 Until user agents allow users to control blinking, avoid causing
content to blink (i.e., change presentation at a regular rate,
such as turning on and off). [Priority 2]
Techniques for checkpoint 7.2
7.3 Until user agents allow users to freeze moving content, avoid
movement in pages. [Priority 2]
When a page includes moving content, provide a mechanism within
a script or applet to allow users to freeze motion or updates.
Using style sheets with scripting to create movement allows
users to turn off or override the effect more easily. Refer
also to guideline 8.
Techniques for checkpoint 7.3
7.4 Until user agents provide the ability to stop the refresh, do not
create periodically auto-refreshing pages. [Priority 2]
For example, in HTML, don't cause pages to auto-refresh with
"HTTP-EQUIV=refresh" until user agents allow users to turn off
the feature.
Techniques for checkpoint 7.4
7.5 Until user agents provide the ability to stop auto-redirect, do
not use markup to redirect pages automatically. Instead,
configure the server to perform redirects. [Priority 2]
Techniques for checkpoint 7.5
Note. The BLINK and MARQUEE elements are not defined in any W3C HTML
specification and should not be used. Refer also to guideline 11.
Guideline 8. Ensure direct accessibility of embedded user interfaces.
Next guideline: 9 Previous guideline: 7 Go to contents
Ensure that the user interface follows principles of accessible design:
device-independent access to functionality, keyboard operability,
self-voicing, etc.
When an embedded object has its "own interface", the interface -- like
the interface to the browser itself -- must be accessible. If the
interface of the embedded object cannot be made accessible, an
alternative accessible solution must be provided.
Note. For information about accessible interfaces, please consult the
User Agent Accessibility Guidelines ([WAI-USERAGENT]) and the
Authoring Tool Accessibility Guidelines ([WAI-AUTOOL]).
Checkpoint:
8.1 Make programmatic elements such as scripts and applets directly
accessible or compatible with assistive technologies
[Priority 1 if functionality is important and not presented
elsewhere, otherwise Priority 2.]
Refer also to guideline 6.
Techniques for checkpoint 8.1
Guideline 9. Design for device-independence.
Next guideline: 10 Previous guideline: 8 Go to contents
Use features that enable activation of page elements via a variety of input
devices.
Device-independent access means that the user may interact with the
user agent or document with a preferred input (or output) device --
mouse, keyboard, voice, head wand, or other. If, for example, a form
control can only be activated with a mouse or other pointing device,
someone who is using the page without sight, with voice input, or with
a keyboard or who is using some other non-pointing input device will
not be able to use the form.
Note. Providing text equivalents for image maps or images used as
links makes it possible for users to interact with them without a
pointing device. Refer also to guideline 1.
Generally, pages that allow keyboard interaction are also accessible
through speech input or a command line interface.
Checkpoints:
9.1 Provide client-side image maps instead of server-side image maps
except where the regions cannot be defined with an available
geometric shape. [Priority 1]
Refer also to checkpoint 1.1, checkpoint 1.2, and checkpoint
1.5.
Techniques for checkpoint 9.1
9.2 Ensure that any element that has its own interface can be operated
in a device-independent manner. [Priority 2]
Refer to the definition of device independence.
Refer also to guideline 8.
Techniques for checkpoint 9.2
9.3 For scripts, specify logical event handlers rather than
device-dependent event handlers. [Priority 2]
Techniques for checkpoint 9.3
9.4 Create a logical tab order through links, form controls, and
objects. [Priority 3]
For example, in HTML, specify tab order via the "tabindex"
attribute or ensure a logical page design.
Techniques for checkpoint 9.4
9.5 Provide keyboard shortcuts to important links (including those in
client-side image maps), form controls, and groups of form
controls. [Priority 3]
For example, in HTML, specify shortcuts via the "accesskey"
attribute.
Techniques for checkpoint 9.5
Guideline 10. Use interim solutions.
Next guideline: 11 Previous guideline: 9 Go to contents
Use interim accessibility solutions so that assistive technologies and
older browsers will operate correctly.
For example, older browsers do not allow users to navigate to empty
edit boxes. Older screen readers read lists of consecutive links as
one link. These active elements are therefore difficult or impossible
to access. Also, changing the current window or popping up new windows
can be very disorienting to users who cannot see that this has
happened.
Note. The following checkpoints apply until user agents (including
assistive technologies) address these issues. These checkpoints are
classified as "interim", meaning that the Web Content Guidelines
Working Group considers them to be valid and necessary to Web
accessibility as of the publication of this document. However, the
Working Group does not expect these checkpoints to be necessary in the
future, once Web technologies have incorporated anticipated features
or capabilities.
Checkpoints:
10.1 Until user agents allow users to turn off spawned windows, do not
cause pop-ups or other windows to appear and do not change the
current window without informing the user. [Priority 2]
For example, in HTML, avoid using a frame whose target is a new
window.
Techniques for checkpoint 10.1
10.2 Until user agents support explicit associations between labels
and form controls, for all form controls with implicitly
associated labels, ensure that the label is properly
positioned. [Priority 2]
The label must immediately precede its control on the same line
(allowing more than one control/label per line) or be in the
line preceding the control (with only one label and one control
per line). Refer also to checkpoint 12.4.
Techniques for checkpoint 10.2
10.3 Until user agents (including assistive technologies) render
side-by-side text correctly, provide a linear text alternative
(on the current page or some other) for all tables that lay out
text in parallel, word-wrapped columns. [Priority 3]
Note. Please consult the definition of linearized table. This
checkpoint benefits people with user agents (such as some
screen readers) that are unable to handle blocks of text
presented side-by-side; the checkpoint should not discourage
content developers from using tables to represent tabular
information.
Techniques for checkpoint 10.3
10.4 Until user agents handle empty controls correctly, include
default, place-holding characters in edit boxes and text areas.
[Priority 3]
For example, in HTML, do this for TEXTAREA and INPUT.
Techniques for checkpoint 10.4
10.5 Until user agents (including assistive technologies) render
adjacent links distinctly, include non-link, printable
characters (surrounded by spaces) between adjacent links.
[Priority 3]
Techniques for checkpoint 10.5
Guideline 11. Use W3C technologies and guidelines.
Next guideline: 12 Previous guideline: 10 Go to contents
Use W3C technologies (according to specification) and follow accessibility
guidelines. Where it is not possible to use a W3C technology, or doing so
results in material that does not transform gracefully, provide an
alternative version of the content that is accessible.
The current guidelines recommend W3C technologies (e.g., HTML, CSS,
etc.) for several reasons:
* W3C technologies include "built-in" accessibility features.
* W3C specifications undergo early review to ensure that
accessibility issues are considered during the design phase.
* W3C specifications are developed in an open, industry consensus
process.
Many non-W3C formats (e.g., PDF, Shockwave, etc.) require viewing with
either plug-ins or stand-alone applications. Often, these formats
cannot be viewed or navigated with standard user agents (including
assistive technologies). Avoiding non-W3C and non-standard features
(proprietary elements, attributes, properties, and extensions) will
tend to make pages more accessible to more people using a wider
variety of hardware and software. When inaccessible technologies
(proprietary or not) must be used, equivalent accessible pages must be
provided.
Even when W3C technologies are used, they must be used in accordance
with accessibility guidelines. When using new technologies, ensure
that they transform gracefully (Refer also to guideline 6.).
Note. Converting documents (from PDF, PostScript, RTF, etc.) to W3C
markup languages (HTML, XML) does not always create an accessible
document. Therefore, validate each page for accessibility and
usability after the conversion process (refer to the section on
validation). If a page does not readily convert, either revise the
page until its original representation converts appropriately or
provide an HTML or plain text version.
Checkpoints:
11.1 Use W3C technologies when they are available and appropriate for
a task and use the latest versions when supported. [Priority 2]
Refer to the list of references for information about where to
find the latest W3C specifications and [WAI-UA-SUPPORT] for
information about user agent support for W3C technologies.
Techniques for checkpoint 11.1
11.2 Avoid deprecated features of W3C technologies. [Priority 2]
For example, in HTML, don't use the deprecated FONT element;
use style sheets instead (e.g., the 'font' property in CSS).
Techniques for checkpoint 11.2
11.3 Provide information so that users may receive documents according
to their preferences (e.g., language, content type, etc.)
[Priority 3]
Note. Use content negotiation where possible.
Techniques for checkpoint 11.3
11.4 If, after best efforts, you cannot create an accessible page,
provide a link to an alternative page that uses W3C
technologies, is accessible, has equivalent information (or
functionality), and is updated as often as the inaccessible
(original) page. [Priority 1]
Techniques for checkpoint 11.4
Note. Content developers should only resort to alternative pages when
other solutions fail because alternative pages are generally updated
less often than "primary" pages. An out-of-date page may be as
frustrating as one that is inaccessible since, in both cases, the
information presented on the original page is unavailable.
Automatically generating alternative pages may lead to more frequent
updates, but content developers must still be careful to ensure that
generated pages always make sense, and that users are able to navigate
a site by following links on primary pages, alternative pages, or
both. Before resorting to an alternative page, reconsider the design
of the original page; making it accessible is likely to improve it for
all users.
Guideline 12. Provide context and orientation information.
Next guideline: 13 Previous guideline: 11 Go to contents
Provide context and orientation information to help users understand
complex pages or elements.
Grouping elements and providing contextual information about the
relationships between elements can be useful for all users. Complex
relationships between parts of a page may be difficult for people with
cognitive disabilities and people with visual disabilities to
interpret.
Checkpoints:
12.1 Title each frame to facilitate frame identification and
navigation. [Priority 1]
For example, in HTML use the "title" attribute on FRAME
elements.
Techniques for checkpoint 12.1
12.2 Describe the purpose of frames and how frames relate to each
other if it is not obvious by frame titles alone. [Priority 2]
For example, in HTML, use "longdesc," or a description link.
Techniques for checkpoint 12.2
12.3 Divide large blocks of information into more manageable groups
where natural and appropriate. [Priority 2]
For example, in HTML, use OPTGROUP to group OPTION elements
inside a SELECT; group form controls with FIELDSET and LEGEND;
use nested lists where appropriate; use headings to structure
documents, etc. Refer also to guideline 3.
Techniques for checkpoint 12.3
12.4 Associate labels explicitly with their controls. [Priority 2]
For example, in HTML use LABEL and its "for" attribute.
Techniques for checkpoint 12.4
Guideline 13. Provide clear navigation mechanisms.
Next guideline: 14 Previous guideline: 12 Go to contents
Provide clear and consistent navigation mechanisms -- orientation
information, navigation bars, a site map, etc. -- to increase the
likelihood that a person will find what they are looking for at a site.
Clear and consistent navigation mechanisms are important to people
with cognitive disabilities or blindness, and benefit all users.
Checkpoints:
13.1 Clearly identify the target of each link. [Priority 2]
Link text should be meaningful enough to make sense when read
out of context -- either on its own or as part of a sequence of
links. Link text should also be terse.
For example, in HTML, write "Information about version 4.3"
instead of "click here". In addition to clear link text,
content developers may further clarify the target of a link
with an informative link title (e.g., in HTML, the "title"
attribute).
Techniques for checkpoint 13.1
13.2 Provide metadata to add semantic information to pages and sites.
[Priority 2]
For example, use RDF ([RDF]) to indicate the document's author,
the type of content, etc.
Note. Some HTML user agents can build navigation tools from
document relations described by the HTML LINK element and "rel"
or "rev" attributes (e.g., rel="next", rel="previous",
rel="index", etc.). Refer also to checkpoint 13.5.
Techniques for checkpoint 13.2
13.3 Provide information about the general layout of a site (e.g., a
site map or table of contents). [Priority 2]
In describing site layout, highlight and explain available
accessibility features.
Techniques for checkpoint 13.3
13.4 Use navigation mechanisms in a consistent manner. [Priority 2]
Techniques for checkpoint 13.4
13.5 Provide navigation bars to highlight and give access to the
navigation mechanism. [Priority 3]
Techniques for checkpoint 13.5
13.6 Group related links, identify the group (for user agents), and,
until user agents do so, provide a way to bypass the group.
[Priority 3]
Techniques for checkpoint 13.6
13.7 If search functions are provided, enable different types of
searches for different skill levels and preferences.
[Priority 3]
Techniques for checkpoint 13.7
13.8 Place distinguishing information at the beginning of headings,
paragraphs, lists, etc. [Priority 3]
Note. This is commonly referred to as "front-loading" and is
especially helpful for people accessing information with serial
devices such as speech synthesizers.
Techniques for checkpoint 13.8
13.9 Provide information about document collections (i.e., documents
comprising multiple pages.). [Priority 3]
For example, in HTML specify document collections with the LINK
element and the "rel" and "rev" attributes. Another way to
create a collection is by building an archive (e.g., with zip,
tar and gzip, stuffit, etc.) of the multiple pages.
Note. The performance improvement gained by offline processing
can make browsing much less expensive for people with
disabilities who may be browsing slowly.
Techniques for checkpoint 13.9
13.10 Provide a means to skip over multi-line ASCII art. [Priority 3]
Refer to checkpoint 1.1 and the example of ascii art in the
glossary.
Techniques for checkpoint 13.10
Guideline 14. Ensure that documents are clear and simple.
Next guideline: 1 Previous guideline: 13 Go to contents
Ensure that documents are clear and simple so they may be more easily
understood.
Consistent page layout, recognizable graphics, and easy to understand
language benefit all users. In particular, they help people with
cognitive disabilities or who have difficulty reading. (However,
ensure that images have text equivalents for people who are blind,
have low vision, or for any user who cannot or has chosen not to view
graphics. Refer also to guideline 1.)
Using clear and simple language promotes effective communication.
Access to written information can be difficult for people who have
cognitive or learning disabilities. Using clear and simple language
also benefits people whose first language differs from your own,
including those people who communicate primarily in sign language.
Checkpoints:
14.1 Use the clearest and simplest language appropriate for a site's
content. [Priority 1]
Techniques for checkpoint 14.1
14.2 Supplement text with graphic or auditory presentations where they
will facilitate comprehension of the page. [Priority 3]
Refer also to guideline 1.
Techniques for checkpoint 14.2
14.3 Create a style of presentation that is consistent across pages.
[Priority 3]
Techniques for checkpoint 14.3
Appendix A. -- Validation
Validate accessibility with automatic tools and human review.
Automated methods are generally rapid and convenient but cannot
identify all accessibility issues. Human review can help ensure
clarity of language and ease of navigation.
Begin using validation methods at the earliest stages of development.
Accessibility issues identified early are easier to correct and avoid.
Following are some important validation methods, discussed in more
detail in the section on validation in the Techniques Document.
1. Use an automated accessibility tool and browser validation tool.
Please note that software tools do not address all accessibility
issues, such as the meaningfulness of link text, the applicability
of a text equivalent, etc.
2. Validate syntax (e.g., HTML, XML, etc.).
3. Validate style sheets (e.g., CSS).
4. Use a text-only browser or emulator.
5. Use multiple graphic browsers, with:
+ sounds and graphics loaded,
+ graphics not loaded,
+ sounds not loaded,
+ no mouse,
+ frames, scripts, style sheets, and applets not loaded
6. Use several browsers, old and new.
7. Use a self-voicing browser, a screen reader, magnification
software, a small display, etc.
8. Use spell and grammar checkers. A person reading a page with a
speech synthesizer may not be able to decipher the synthesizer's
best guess for a word with a spelling error. Eliminating grammar
problems increases comprehension.
9. Review the document for clarity and simplicity. Readability
statistics, such as those generated by some word processors may be
useful indicators of clarity and simplicity. Better still, ask an
experienced (human) editor to review written content for clarity.
Editors can also improve the usability of documents by identifying
potentially sensitive cultural issues that might arise due to
language or icon usage.
10. Invite people with disabilities to review documents. Expert and
novice users with disabilities will provide valuable feedback
about accessibility or usability problems and their severity.
Appendix B. -- Glossary
Accessible
Content is accessible when it may be used by someone with a
disability.
Applet
A program inserted into a Web page.
Assistive technology
Software or hardware that has been specifically designed to
assist people with disabilities in carrying out daily
activities. Assistive technology includes wheelchairs, reading
machines, devices for grasping, etc. In the area of Web
Accessibility, common software-based assistive technologies
include screen readers, screen magnifiers, speech synthesizers,
and voice input software that operate in conjunction with
graphical desktop browsers (among other user agents). Hardware
assistive technologies include alternative keyboards and
pointing devices.
Authoring tool
HTML editors, document conversion tools, tools that generate
Web content from databases are all authoring tools. Refer to
the "Authoring Tool Accessibility Guidelines" ([WAI-AUTOOLS])
for information about developing accessible tools.
Backward compatible
Design that continues to work with earlier versions of a
language, program, etc.
Braille
Braille uses six raised dots in different patterns to represent
letters and numbers to be read by people who are blind with
their fingertips. The word "Accessible" in braille follows:
Accessible
A braille display, commonly referred to as a "dynamic braille
display," raises or lowers dot patterns on command from an
electronic device, usually a computer. The result is a line of
braille that can change from moment to moment. Current dynamic
braille displays range in size from one cell (six or eight
dots) to an eighty-cell line, most having between twelve and
twenty cells per line.
Content developer
Someone who authors Web pages or designs Web sites.
Deprecated
A deprecated element or attribute is one that has been outdated
by newer constructs. Deprecated elements may become obsolete in
future versions of HTML. The index of HTML elements and
attributes in the Techniques Document indicates which elements
and attributes are deprecated in HTML 4.0.
Authors should avoid using deprecated elements and attributes.
User agents should continue to support for reasons of backward
compatibility.
Device independent
Users must be able to interact with a user agent (and the
document it renders) using the supported input and output
devices of their choice and according to their needs. Input
devices may include pointing devices, keyboards, braille
devices, head wands, microphones, and others. Output devices
may include monitors, speech synthesizers, and braille devices.
Please note that "device-independent support" does not mean
that user agents must support every input or output device.
User agents should offer redundant input and output mechanisms
for those devices that are supported. For example, if a user
agent supports keyboard and mouse input, users should be able
to interact with all features using either the keyboard or the
mouse.
Document Content, Structure, and Presentation
The content of a document refers to what it says to the user
through natural language, images, sounds, movies, animations,
etc. The structure of a document is how it is organized
logically (e.g., by chapter, with an introduction and table of
contents, etc.). An element (e.g., P, STRONG, BLOCKQUOTE in
HTML) that specifies document structure is called a structural
element. The presentation of a document is how the document is
rendered (e.g., as print, as a two-dimensional graphical
presentation, as an text-only presentation, as synthesized
speech, as braille, etc.) An element that specifies document
presentation (e.g., B, FONT, CENTER) is called a presentation
element.
Consider a document header, for example. The content of the
header is what the header says (e.g., "Sailboats"). In HTML,
the header is a structural element marked up with, for example,
an H2 element. Finally, the presentation of the header might be
a bold block text in the margin, a centered line of text, a
title spoken with a certain voice style (like an aural font),
etc.
Dynamic HTML (DHTML)
DHTML is the marketing term applied to a mixture of standards
including HTML, style sheets, the Document Object Model [DOM1]
and scripting. However, there is no W3C specification that
formally defines DHTML. Most guidelines may be applicable to
applications using DHTML, however the following guidelines
focus on issues related to scripting and style sheets:
guideline 1, guideline 3, guideline 6, guideline 7, and
guideline 9.
Element
This document uses the term "element" both in the strict SGML
sense (an element is a syntactic construct) and more generally
to mean a type of content (such as video or sound) or a logical
construct (such as a header or list). The second sense
emphasizes that a guideline inspired by HTML could easily apply
to another markup language.
Note that some (SGML) elements have content that is rendered
(e.g., the P, LI, or TABLE elements in HTML), some are replaced
by external content (e.g., IMG), and some affect processing
(e.g., STYLE and SCRIPT cause information to be processed by a
style sheet or script engine). An element that causes text
characters to be part of the document is called a text element.
Equivalent
Content is "equivalent" to other content when both fulfill
essentially the same function or purpose upon presentation to
the user. In the context of this document, the equivalent must
fulfill essentially the same function for the person with a
disability (at least insofar as is feasible, given the nature
of the disability and the state of technology), as the primary
content does for the person without any disability. For
example, the text "The Full Moon" might convey the same
information as an image of a full moon when presented to users.
Note that equivalent information focuses on fulfilling the same
function. If the image is part of a link and understanding the
image is crucial to guessing the link target, an equivalent
must also give users an idea of the link target. Providing
equivalent information for inaccessible content is one of the
primary ways authors can make their documents accessible to
people with disabilities.
As part of fulfilling the same function of content an
equivalent may involve a description of that content (i.e.,
what the content looks like or sounds like). For example, in
order for users to understand the information conveyed by a
complex chart, authors should describe the visual information
in the chart.
Since text content can be presented to the user as synthesized
speech, braille, and visually-displayed text, these guidelines
require text equivalents for graphic and audio information.
Text equivalents must be written so that they convey all
essential content. Non-text equivalents (e.g., an auditory
description of a visual presentation, a video of a person
telling a story using sign language as an equivalent for a
written story, etc.) also improve accessibility for people who
cannot access visual information or written text, including
many individuals with blindness, cognitive disabilities,
learning disabilities, and deafness.
Equivalent information may be provided in a number of ways,
including through attributes (e.g., a text value for the "alt"
attribute in HTML and SMIL), as part of element content (e.g.,
the OBJECT in HTML), as part of the document's prose, or via a
linked document (e.g., designated by the "longdesc" attribute
in HTML or a description link). Depending on the complexity of
the equivalent, it may be necessary to combine techniques
(e.g., use "alt" for an abbreviated equivalent, useful to
familiar readers, in addition to "longdesc" for a link to more
complete information, useful to first-time readers). The
details of how and when to provide equivalent information are
part of the Techniques Document ([TECHNIQUES]).
A text transcript is a text equivalent of audio information
that includes spoken words and non-spoken sounds such as sound
effects. A caption is a text transcript for the audio track of
a video presentation that is synchronized with the video and
audio tracks. Captions are generally rendered visually by being
superimposed over the video, which benefits people who are deaf
and hard-of-hearing, and anyone who cannot hear the audio
(e.g., when in a crowded room). A collated text transcript
combines (collates) captions with text descriptions of video
information (descriptions of the actions, body language,
graphics, and scene changes of the video track). These text
equivalents make presentations accessible to people who are
deaf-blind and to people who cannot play movies, animations,
etc. It also makes the information available to search engines.
One example of a non-text equivalent is an auditory description
of the key visual elements of a presentation. The description
is either a prerecorded human voice or a synthesized voice
(recorded or generated on the fly). The auditory description is
synchronized with the audio track of the presentation, usually
during natural pauses in the audio track. Auditory descriptions
include information about actions, body language, graphics, and
scene changes.
Image
A graphical presentation.
Image map
An image that has been divided into regions with associated
actions. Clicking on an active region causes an action to
occur.
When a user clicks on an active region of a client-side image
map, the user agent calculates in which region the click
occurred and follows the link associated with that region.
Clicking on an active region of a server-side image map causes
the coordinates of the click to be sent to a server, which then
performs some action.
Content developers can make client-side image maps accessible
by providing device-independent access to the same links
associated with the image map's regions. Client-side image maps
allow the user agent to provide immediate feedback as to
whether or not the user's pointer is over an active region.
Important
Information in a document is important if understanding that
information is crucial to understanding the document.
Linearized table
A table rendering process where the contents of the cells
become a series of paragraphs (e.g., down the page) one after
another. The paragraphs will occur in the same order as the
cells are defined in the document source. Cells should make
sense when read in order and should include structural elements
(that create paragraphs, headers, lists, etc.) so the page
makes sense after linearization.
Link text
The rendered text content of a link.
Natural Language
Spoken, written, or signed human languages such as French,
Japanese, American Sign Language, and braille. The natural
language of content may be indicated with the "lang" attribute
in HTML ([HTML40], section 8.1) and the "xml:lang" attribute in
XML ([XML], section 2.12).
Navigation Mechanism
A navigation mechanism is any means by which a user can
navigate a page or site. Some typical mechanisms include:
navigation bars
A navigation bar is a collection of links to the most
important parts of a document or site.
site maps
A site map provides a global view of the organization of
a page or site.
tables of contents
A table of contents generally lists (and links to) the
most important sections of a document.
Personal Digital Assistant (PDA)
A PDA is a small, portable computing device. Most PDAs are used
to track personal data such as calendars, contacts, and
electronic mail. A PDA is generally a handheld device with a
small screen that allows input from various sources.
Screen magnifier
A software program that magnifies a portion of the screen, so
that it can be more easily viewed. Screen magnifiers are used
primarily by individuals with low vision.
Screen reader
A software program that reads the contents of the screen aloud
to a user. Screen readers are used primarily by individuals who
are blind. Screen readers can usually only read text that is
printed, not painted, to the screen.
Style sheets
A style sheet is a set of statements that specify presentation
of a document. Style sheets may have three different origins:
they may be written by content providers, created by users, or
built into user agents. In CSS ([CSS2]), the interaction of
content provider, user, and user agent style sheets is called
the cascade.
Presentation markup is markup that achieves a stylistic (rather
than structuring) effect such as the B or I elements in HTML.
Note that the STRONG and EM elements are not considered
presentation markup since they convey information that is
independent of a particular font style.
Tabular information
When tables are used to represent logical relationships among
data -- text, numbers, images, etc., that information is called
"tabular information" and the tables are called "data tables".
The relationships expressed by a table may be rendered visually
(usually on a two-dimensional grid), aurally (often preceding
cells with header information), or in other formats.
Until user agents ...
In most of the checkpoints, content developers are asked to
ensure the accessibility of their pages and sites. However,
there are accessibility needs that would be more appropriately
met by user agents (including assistive technologies). As of
the publication of this document, not all user agents or
assistive technologies provide the accessibility control users
require (e.g., some user agents may not allow users to turn off
blinking content, or some screen readers may not handle tables
well). Checkpoints that contain the phrase "until user agents
..." require content developers to provide additional support
for accessibility until most user agents readily available to
their audience include the necessary accessibility features.
Note. The W3C WAI Web site (refer to [WAI-UA-SUPPORT]) provides
information about user agent support for accessibility
features. Content developers are encouraged to consult this
page regularly for updated information.
User agent
Software to access Web content, including desktop graphical
browsers, text browsers, voice browsers, mobile phones,
multimedia players, plug-ins, and some software assistive
technologies used in conjunction with browsers such as screen
readers, screen magnifiers, and voice recognition software.
