FYI - In regard to ADA compliance, we
suggest that the institution receive some type of assurance from its
web site developers
(informational, Internet, mobile banking, etc.) that the developers
are following the Web Continent Accessibility Guidelines (WCAG) 2.0
coding guidelines.
[contents]
Web Content Accessibility
Guidelines (WCAG) 2.0
W3C
Recommendation 11 December 2008
- This version:
-
http://www.w3.org/TR/2008/REC-WCAG20-20081211/
- Latest version:
-
http://www.w3.org/TR/WCAG20/
- Previous version:
-
http://www.w3.org/TR/2008/PR-WCAG20-20081103/
- Editors:
- Ben Caldwell, Trace R&D Center, University of
Wisconsin-Madison
- Michael Cooper, W3C
- Loretta Guarino Reid, Google, Inc.
- Gregg Vanderheiden, Trace R&D Center, University of
Wisconsin-Madison
- Previous Editors:
- Wendy Chisholm (until July 2006 while at W3C)
- John Slatin (until June 2006 while at Accessibility
Institute, University of Texas at Austin)
- Jason White (until June 2005 while at University of
Melbourne)
Please refer to the
errata
for this document, which may include normative corrections.
See also
translations.
This document is also available in non-normative formats,
available from
Alternate Versions of Web Content Accessibility Guidelines 2.0.
Copyright © 2008
W3C®
(MIT,
ERCIM, Keio),
All Rights Reserved. W3C
liability,
trademark and
document use rules apply.
Abstract
Web Content Accessibility Guidelines (WCAG) 2.0 covers a wide
range of recommendations for making Web content more accessible.
Following these guidelines will make content accessible to a
wider range of people with disabilities, including blindness and
low vision, deafness and hearing loss, learning disabilities,
cognitive limitations, limited movement, speech disabilities,
photosensitivity and combinations of these. Following these
guidelines will also often make your Web content more usable to
users in general.
WCAG 2.0 success criteria are written as testable statements
that are not technology-specific. Guidance about satisfying the
success criteria in specific technologies, as well as general
information about interpreting the success criteria, is provided
in separate documents. See
Web Content
Accessibility Guidelines (WCAG) Overview for an introduction
and links to WCAG technical and educational material.
WCAG 2.0 succeeds
Web Content Accessibility
Guidelines 1.0
[WCAG10], which was published as a W3C Recommendation May
1999. Although it is possible to conform either to WCAG 1.0 or
to WCAG 2.0 (or both), the W3C recommends that new and updated
content use WCAG 2.0. The W3C also recommends that Web
accessibility policies reference WCAG 2.0.
Status of this Document
This section describes the status of this document at the
time of its publication. Other documents may supersede this
document. A list of current W3C publications and the latest
revision of this technical report can be found in the
W3C technical reports index
at http://www.w3.org/TR/.
This is the Web Content Accessibility Guidelines (WCAG) 2.0
W3C Recommendation from the
Web Content Accessibility
Guidelines Working Group.
This document has been reviewed by W3C Members, by software
developers, and by other W3C groups and interested parties, and
is endorsed by the Director as a W3C Recommendation. It is a
stable document and may be used as reference material or cited
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.
WCAG 2.0 is supported by the associated non-normative
documents,
Understanding WCAG 2.0 and
Techniques for WCAG
2.0. Although those documents do not have the formal status
that WCAG 2.0 itself has, they provide information important to
understanding and implementing WCAG.
The Working Group requests that any comments be made using
the provided
online comment form. If this is not possible, comments can
also be sent to
public-comments-wcag20@w3.org. The
archives for the public comments list are publicly
available. Comments received on the WCAG 2.0 Recommendation
cannot result in changes to this version of the guidelines, but
may be addressed in errata or future versions of WCAG. The
Working Group does not plan to make formal responses to
comments. Archives of the
WCAG
WG mailing list discussions are publicly available, and
future work undertaken by the Working Group may address comments
received on this document.
This document has been produced as part of the W3C
Web Accessibility Initiative
(WAI). The goals of the WCAG Working Group are discussed in the
WCAG Working
Group charter. The WCAG Working Group is part of the
WAI Technical
Activity.
This document was produced by a group operating under the
5
February 2004 W3C Patent Policy. W3C maintains a
public list of any patent disclosures made in connection
with the deliverables of the group; that page also includes
instructions for disclosing a patent. An individual who has
actual knowledge of a patent which the individual believes
contains
Essential Claim(s) must disclose the information in
accordance with
section 6 of the W3C Patent Policy.
Table of Contents
Appendices
Introduction
This section is
informative.
Web Content Accessibility Guidelines (WCAG) 2.0 defines
how to make Web content more accessible to people with
disabilities. Accessibility involves a wide range of
disabilities, including visual, auditory, physical, speech,
cognitive, language, learning, and neurological
disabilities. Although these guidelines cover a wide range
of issues, they are not able to address the needs of people
with all types, degrees, and combinations of disability.
These guidelines also make Web content more usable by older
individuals with changing abilities due to aging and often
improve usability for users in general.
WCAG 2.0 is developed through the
W3C
process in cooperation with individuals and
organizations around the world, with a goal of providing a
shared standard for Web content accessibility that meets the
needs of individuals, organizations, and governments
internationally. WCAG 2.0 builds on WCAG 1.0
[WCAG10]
and is designed to apply broadly to different Web
technologies now and in the future, and to be testable with
a combination of automated testing and human evaluation. For
an introduction to WCAG, see the
Web Content
Accessibility Guidelines (WCAG) Overview.
Web accessibility depends not only on accessible content
but also on accessible Web browsers and other user agents.
Authoring tools also have an important role in Web
accessibility. For an overview of how these components of
Web development and interaction work together, see:
WCAG 2.0 Layers of Guidance
The individuals and organizations that use WCAG vary
widely and include Web designers and developers, policy
makers, purchasing agents, teachers, and students. In
order to meet the varying needs of this audience,
several layers of guidance are provided including
overall principles, general guidelines,
testable success criteria and a rich collection
of sufficient techniques, advisory techniques,
and documented common failures with examples,
resource links and code.
-
Principles - At the top are four
principles that provide the foundation for Web
accessibility: perceivable, operable,
understandable, and robust. See also
Understanding the Four Principles of Accessibility.
-
Guidelines - Under the
principles are guidelines. The 12 guidelines provide
the basic goals that authors should work toward in
order to make content more accessible to users with
different disabilities. The guidelines are not
testable, but provide the framework and overall
objectives to help authors understand the success
criteria and better implement the techniques.
-
Success Criteria - For each
guideline, testable success criteria are provided to
allow WCAG 2.0 to be used where requirements and
conformance testing are necessary such as in design
specification, purchasing, regulation, and
contractual agreements. In order to meet the needs
of different groups and different situations, three
levels of conformance are defined: A (lowest), AA,
and AAA (highest). Additional information on WCAG
levels can be found in
Understanding Levels of Conformance.
-
Sufficient and Advisory Techniques
- For each of the guidelines and
success criteria in the WCAG 2.0 document
itself, the working group has also documented a wide
variety of techniques. The techniques are
informative and fall into two categories: those that
are sufficient for meeting the success
criteria and those that are advisory. The
advisory techniques go beyond what is required by
the individual success criteria and allow authors to
better address the guidelines. Some advisory
techniques address accessibility barriers that are
not covered by the testable success criteria. Where
common failures are known, these are also
documented. See also
Sufficient and Advisory Techniques in Understanding
WCAG 2.0.
All of these layers of guidance (principles,
guidelines, success criteria, and sufficient and
advisory techniques) work together to provide guidance
on how to make content more accessible. Authors are
encouraged to view and apply all layers that they are
able to, including the advisory techniques, in order to
best address the needs of the widest possible range of
users.
Note that even content that conforms at the highest
level (AAA) will not be accessible to individuals with
all types, degrees, or combinations of disability,
particularly in the cognitive language and learning
areas. Authors are encouraged to consider the full range
of techniques, including the advisory techniques, as
well as to seek relevant advice about current best
practice to ensure that Web content is accessible, as
far as possible, to this community.
Metadata may assist users in finding content most
suitable for their needs.
WCAG 2.0 Supporting Documents
The WCAG 2.0 document is designed to meet the needs
of those who need a stable, referenceable technical
standard. Other documents, called supporting documents,
are based on the WCAG 2.0 document and address other
important purposes, including the ability to be updated
to describe how WCAG would be applied with new
technologies. Supporting documents include:
-
How
to Meet WCAG 2.0 - A customizable quick
reference to WCAG 2.0 that includes all of the
guidelines, success criteria, and techniques for
authors to use as they are developing and evaluating
Web content.
-
Understanding WCAG 2.0 - A guide to
understanding and implementing WCAG 2.0. There is a
short "Understanding" document for each guideline
and success criterion in WCAG 2.0 as well as key
topics.
-
Techniques for WCAG 2.0 - A collection
of techniques and common failures, each in a
separate document that includes a description,
examples, code and tests.
-
The
WCAG 2.0 Documents - A diagram and
description of how the technical documents are
related and linked.
See
Web Content Accessibility Guidelines (WCAG) Overview
for a description of the WCAG 2.0 supporting material,
including education resources related to WCAG 2.0.
Additional resources covering topics such as the
business case for Web accessibility, planning
implementation to improve the accessibility of Web
sites, and accessibility policies are listed in
WAI
Resources.
Important
Terms in WCAG 2.0
WCAG 2.0 includes three important terms that are
different from WCAG 1.0. Each of these is introduced
briefly below and defined more fully in the glossary.
- Web Page
-
It is important to note that, in this standard,
the term "Web
page" includes much more than static HTML pages.
It also includes the increasingly dynamic Web pages
that are emerging on the Web, including "pages" that
can present entire virtual interactive communities.
For example, the term "Web page" includes an
immersive, interactive movie-like experience found
at a single URI. For more information, see
Understanding "Web Page".
- Programmatically Determined
-
Several success criteria require that content (or
certain aspects of content) can be "programmatically
determined." This means that the content is
delivered in such a way that
user agents, including
assistive technologies, can extract and present
this information to users in different modalities.
For more information, see
Understanding Programmatically Determined.
- Accessibility Supported
-
Using a technology in a way that is accessibility
supported means that it works with assistive
technologies (AT) and the accessibility features of
operating systems, browsers, and other user agents.
Technology features can only be
relied upon to conform to WCAG 2.0 success
criteria if they are used in a way that is "accessibility
supported". Technology features can be used in
ways that are not accessibility supported (do not
work with assistive technologies, etc.) as long as
they are not relied upon to conform to any success
criterion (i.e., the same information or
functionality is also available another way that is
supported).
The definition of "accessibility supported" is
provided in the
Appendix A: Glossary section of these
guidelines. For more information, see
Understanding Accessibility Support.
WCAG 2.0
Guidelines
This section is
normative.
Principle 1:
Perceivable - Information and user interface components
must be presentable to users in ways they can perceive.
Guideline 1.1 Text Alternatives: Provide text
alternatives for any non-text content so that it
can be changed into other forms people need,
such as large print, braille, speech, symbols or
simpler language.
Understanding Guideline 1.1
1.1.1 Non-text
Content: All
non-text content that is presented
to the user has a
text alternative that serves the
equivalent purpose, except for the
situations listed below. (Level A)
-
Controls, Input: If
non-text content is a control or
accepts user input, then it has a
name that describes its purpose.
(Refer to
Guideline 4.1 for additional
requirements for controls and
content that accepts user input.)
-
Time-Based Media: If
non-text content is time-based
media, then text alternatives at
least provide descriptive
identification of the non-text
content. (Refer to
Guideline 1.2 for additional
requirements for media.)
-
Test:
If non-text content is a
test or exercise that would be
invalid if presented in
text, then text alternatives at
least provide descriptive
identification of the non-text
content.
-
Sensory: If non-text
content is primarily intended to
create a
specific sensory experience,
then text alternatives at least
provide descriptive identification
of the non-text content.
-
CAPTCHA: If the purpose
of non-text content is to confirm
that content is being accessed by a
person rather than a computer, then
text alternatives that identify and
describe the purpose of the non-text
content are provided, and
alternative forms of CAPTCHA using
output modes for different types of
sensory perception are provided to
accommodate different disabilities.
-
Decoration, Formatting, Invisible:
If non-text content is
pure decoration, is used only
for visual formatting, or is not
presented to users, then it is
implemented in a way that it can be
ignored by
assistive technology.
Guideline 1.3 Adaptable: Create content that
can be presented in different ways (for example
simpler layout) without losing information or
structure.
Understanding Guideline 1.3
1.3.3 Sensory
Characteristics: Instructions
provided for understanding and operating
content do not rely solely on sensory
characteristics of components such as
shape, size, visual location,
orientation, or sound. (Level A)
Guideline 1.4 Distinguishable: Make it
easier for users to see and hear content
including separating foreground from background.
Understanding Guideline 1.4
1.4.1 Use of
Color: Color is not used as the
only visual means of conveying
information, indicating an action,
prompting a response, or distinguishing
a visual element. (Level A)
Note:
This success criterion addresses
color perception specifically. Other
forms of perception are covered in
Guideline 1.3 including
programmatic access to color and
other visual presentation coding.
1.4.2 Audio
Control: If any audio on a Web
page plays automatically for more than 3
seconds, either a
mechanism is available to pause or
stop the audio, or a mechanism is
available to control audio volume
independently from the overall system
volume level. (Level A)
Note:
Since any content that does not meet
this success criterion can interfere
with a user's ability to use the
whole page, all content on the Web
page (whether or not it is used to
meet other success criteria) must
meet this success criterion. See
Conformance Requirement 5:
Non-Interference.
1.4.3 Contrast
(Minimum): The visual
presentation of
text and
images of text has a
contrast ratio of at least 4.5:1,
except for the following: (Level AA)
-
Large
Text:
Large-scale text and images of
large-scale text have a contrast
ratio of at least 3:1;
-
Incidental: Text or images
of text that are part of an inactive
user interface component, that
are
pure decoration, that are not
visible to anyone, or that are part
of a picture that contains
significant other visual content,
have no contrast requirement.
-
Logotypes: Text that is
part of a logo or brand name has no
minimum contrast requirement.
1.4.5 Images
of Text: If the technologies
being used can achieve the visual
presentation,
text is used to convey information
rather than
images of text except for the
following: (Level AA)
Note:
Logotypes (text that is part of a
logo or brand name) are considered
essential.
1.4.6 Contrast
(Enhanced): The visual
presentation of
text and
images of text has a
contrast ratio of at least 7:1,
except for the following: (Level AAA)
-
Large
Text:
Large-scale text and images of
large-scale text have a contrast
ratio of at least 4.5:1;
-
Incidental: Text or images
of text that are part of an inactive
user interface component, that
are
pure decoration, that are not
visible to anyone, or that are part
of a picture that contains
significant other visual content,
have no contrast requirement.
-
Logotypes: Text that is
part of a logo or brand name has no
minimum contrast requirement.
1.4.7 Low or
No Background Audio: For
prerecorded
audio-only content that (1) contains
primarily speech in the foreground, (2)
is not an audio
CAPTCHA or audio logo, and (3) is
not vocalization intended to be
primarily musical expression such as
singing or rapping, at least one of the
following is true: (Level AAA)
-
No
Background: The audio does
not contain background sounds.
-
Turn
Off: The background sounds
can be turned off.
-
20 dB:
The background sounds are
at least 20 decibels lower than the
foreground speech content, with the
exception of occasional sounds that
last for only one or two seconds.
Note:
Per the definition of
"decibel," background sound that
meets this requirement will be
approximately four times quieter
than the foreground speech
content.
1.4.8 Visual
Presentation: For the visual
presentation of
blocks of text, a
mechanism is available to achieve
the following: (Level AAA)
-
Foreground and background colors
can be selected by the user.
-
Width is no more than 80
characters or glyphs (40 if
CJK).
-
Text is not justified (aligned to
both the left and the right
margins).
-
Line spacing (leading) is at
least space-and-a-half within
paragraphs, and paragraph spacing is
at least 1.5 times larger than the
line spacing.
-
Text can be resized without
assistive technology up to 200
percent in a way that does not
require the user to scroll
horizontally to read a line of text
on a full-screen window.
1.4.9 Images
of Text (No Exception):
Images of text are only used for
pure decoration or where a
particular presentation of
text is
essential to the information being
conveyed. (Level AAA)
Note:
Logotypes (text that is part of a
logo or brand name) are considered
essential.
Principle 2: Operable - User interface components
and navigation must be operable.
2.1.1
Keyboard: All
functionality of the content is
operable through a
keyboard interface without requiring
specific timings for individual
keystrokes, except where the underlying
function requires input that depends on
the path of the user's movement and not
just the endpoints. (Level A)
Note 1:
This exception relates to the
underlying function, not the input
technique. For example, if using
handwriting to enter text, the input
technique (handwriting) requires
path-dependent input but the
underlying function (text input)
does not.
Note 2:
This does not forbid and should not
discourage providing mouse input or
other input methods in addition to
keyboard operation.
2.1.2 No
Keyboard Trap: If keyboard
focus can be moved to a component of the
page using a
keyboard interface, then focus can
be moved away from that component using
only a keyboard interface, and, if it
requires more than unmodified arrow or
tab keys or other standard exit methods,
the user is advised of the method for
moving focus away. (Level A)
Note:
Since any content that does not meet
this success criterion can interfere
with a user's ability to use the
whole page, all content on the Web
page (whether it is used to meet
other success criteria or not) must
meet this success criterion. See
Conformance Requirement 5:
Non-Interference.
2.1.3 Keyboard
(No Exception): All
functionality of the content is
operable through a
keyboard interface without requiring
specific timings for individual
keystrokes. (Level AAA)
2.2.1 Timing
Adjustable: For each time limit
that is set by the content, at least one
of the following is true: (Level A)
-
Turn
off: The user is allowed to
turn off the time limit before
encountering it; or
-
Adjust:
The user is allowed to
adjust the time limit before
encountering it over a wide range
that is at least ten times the
length of the default setting; or
-
Extend:
The user is warned before
time expires and given at least 20
seconds to extend the time limit
with a simple action (for example,
"press the space bar"), and the user
is allowed to extend the time limit
at least ten times; or
-
Real-time Exception: The
time limit is a required part of a
real-time event (for example, an
auction), and no alternative to the
time limit is possible; or
-
Essential Exception: The
time limit is
essential and extending it would
invalidate the activity; or
-
20 Hour
Exception: The time limit
is longer than 20 hours.
Note:
This success criterion helps ensure
that users can complete tasks
without unexpected changes in
content or context that are a result
of a time limit. This success
criterion should be considered in
conjunction with
Success Criterion 3.2.1, which
puts limits on changes of content or
context as a result of user action.
2.2.2 Pause,
Stop, Hide: For moving,
blinking, scrolling, or
auto-updating information, all of the
following are true: (Level A)
-
Moving,
blinking, scrolling: For
any moving, blinking or scrolling
information that (1) starts
automatically, (2) lasts more than
five seconds, and (3) is presented
in parallel with other content,
there is a mechanism for the user to
pause, stop, or hide it unless
the movement, blinking, or scrolling
is part of an activity where it is
essential; and
-
Auto-updating: For any
auto-updating information that (1)
starts automatically and (2) is
presented in parallel with other
content, there is a mechanism for
the user to pause, stop, or hide it
or to control the frequency of the
update unless the auto-updating is
part of an activity where it is
essential.
Note 1:
For requirements related to
flickering or flashing content,
refer to
Guideline 2.3.
Note 2:
Since any content that does not meet
this success criterion can interfere
with a user's ability to use the
whole page, all content on the Web
page (whether it is used to meet
other success criteria or not) must
meet this success criterion. See
Conformance Requirement 5:
Non-Interference.
Note 3:
Content that is updated periodically
by software or that is streamed to
the user agent is not required to
preserve or present information that
is generated or received between the
initiation of the pause and resuming
presentation, as this may not be
technically possible, and in many
situations could be misleading to do
so.
Note 4:
An animation that occurs as part of
a preload phase or similar situation
can be considered essential if
interaction cannot occur during that
phase for all users and if not
indicating progress could confuse
users or cause them to think that
content was frozen or broken.
2.2.4
Interruptions: Interruptions
can be postponed or suppressed by the
user, except interruptions involving an
emergency. (Level AAA)
2.2.5
Re-authenticating: When an
authenticated session expires, the user
can continue the activity without loss
of data after re-authenticating. (Level
AAA)
2.3.1 Three
Flashes or Below Threshold:
Web pages do not contain anything
that flashes more than three times in
any one second period, or the
flash is below the
general flash and red flash thresholds.
(Level A)
Note:
Since any content that does not meet
this success criterion can interfere
with a user's ability to use the
whole page, all content on the Web
page (whether it is used to meet
other success criteria or not) must
meet this success criterion. See
Conformance Requirement 5:
Non-Interference.
2.3.2 Three
Flashes:
Web pages do not contain anything
that
flashes more than three times in any
one second period. (Level AAA)
2.4.1 Bypass
Blocks: A
mechanism is available to bypass
blocks of content that are repeated on
multiple
Web pages. (Level A)
2.4.2 Page
Titled:
Web pages have titles that describe
topic or purpose. (Level A)
2.4.3 Focus
Order: If a
Web page can be
navigated sequentially and the
navigation sequences affect meaning or
operation, focusable components receive
focus in an order that preserves meaning
and operability. (Level A)
2.4.5 Multiple
Ways: More than one way is
available to locate a
Web page within a
set of Web pages except where the
Web Page is the result of, or a step in,
a
process. (Level AA)
2.4.6 Headings
and Labels: Headings and
labels describe topic or purpose.
(Level AA)
2.4.7 Focus
Visible: Any keyboard operable
user interface has a mode of operation
where the keyboard focus indicator is
visible. (Level AA)
2.4.8
Location: Information about the
user's location within a
set of Web pages is available.
(Level AAA)
2.4.9 Link
Purpose (Link Only): A
mechanism is available to allow the
purpose of each link to be identified
from link text alone, except where the
purpose of the link would be
ambiguous to users in general.
(Level AAA)
2.4.10 Section
Headings:
Section headings are used to
organize the content. (Level AAA)
Note 1:
"Heading" is used in its general
sense and includes titles and other
ways to add a heading to different
types of content.
Note 2:
This success criterion covers
sections within writing, not
user interface components. User
Interface components are covered
under
Success Criterion 4.1.2.
Principle 3: Understandable - Information and the
operation of user interface must be understandable.
3.1.2 Language
of Parts: The
human language of each passage or
phrase in the content can be
programmatically determined except
for proper names, technical terms, words
of indeterminate language, and words or
phrases that have become part of the
vernacular of the immediately
surrounding text. (Level AA)
3.1.4
Abbreviations: A
mechanism for identifying the
expanded form or meaning of
abbreviations is available. (Level
AAA)
3.1.5 Reading
Level: When text requires
reading ability more advanced than the
lower secondary education level
after removal of proper names and
titles,
supplemental content, or a version
that does not require reading ability
more advanced than the lower secondary
education level, is available. (Level
AAA)
3.1.6
Pronunciation: A
mechanism is available for
identifying specific pronunciation of
words where meaning of the words, in
context, is ambiguous without knowing
the pronunciation. (Level AAA)
3.2.1 On
Focus: When any component
receives focus, it does not initiate a
change of context. (Level A)
3.2.3
Consistent Navigation:
Navigational mechanisms that are
repeated on multiple
Web pages within a
set of Web pages occur in the
same relative order each time they
are repeated, unless a change is
initiated by the user. (Level AA)
3.2.4
Consistent Identification:
Components that have the
same functionality within a set of
Web pages are identified
consistently. (Level AA)
3.2.5 Change
on Request:
Changes of context are initiated
only by user request or a
mechanism is available to turn off
such changes. (Level AAA)
3.3.1 Error
Identification: If an
input error is automatically
detected, the item that is in error is
identified and the error is described to
the user in text. (Level A)
3.3.2 Labels
or Instructions:
Labels or instructions are provided
when content requires user input. (Level
A)
3.3.3 Error
Suggestion: If an
input error is automatically
detected and suggestions for correction
are known, then the suggestions are
provided to the user, unless it would
jeopardize the security or purpose of
the content. (Level AA)
3.3.4 Error
Prevention (Legal, Financial, Data):
For
Web pages that cause
legal commitments or financial
transactions for the user to occur, that
modify or delete
user-controllable data in data
storage systems, or that submit user
test responses, at least one of the
following is true: (Level AA)
-
Reversible: Submissions are
reversible.
-
Checked: Data entered by
the user is checked for
input errors and the user is
provided an opportunity to correct
them.
-
Confirmed: A
mechanism is available for
reviewing, confirming, and
correcting information before
finalizing the submission.
3.3.6 Error
Prevention (All): For
Web pages that require the user to
submit information, at least one of the
following is true: (Level AAA)
-
Reversible: Submissions are
reversible.
-
Checked: Data entered by
the user is checked for
input errors and the user is
provided an opportunity to correct
them.
-
Confirmed: A
mechanism is available for
reviewing, confirming, and
correcting information before
finalizing the submission.
Principle 4: Robust - Content must be robust enough that
it can be interpreted reliably by a wide variety of user
agents, including assistive technologies.
Guideline 4.1 Compatible: Maximize
compatibility with current and future user
agents, including assistive technologies.
Understanding Guideline 4.1
4.1.1 Parsing:
In content implemented using markup
languages, elements have complete start
and end tags, elements are nested
according to their specifications,
elements do not contain duplicate
attributes, and any IDs are unique,
except where the specifications allow
these features. (Level A)
Note:
Start and end tags that are missing
a critical character in their
formation, such as a closing angle
bracket or a mismatched attribute
value quotation mark are not
complete.
4.1.2 Name,
Role, Value: For all
user interface components (including
but not limited to: form elements, links
and components generated by scripts),
the
name and
role can be
programmatically determined; states,
properties, and values that can be set
by the user can be
programmatically set; and
notification of changes to these items
is available to
user agents, including
assistive technologies. (Level A)
Note:
This success criterion is primarily
for Web authors who develop or
script their own user interface
components. For example, standard
HTML controls already meet this
success criterion when used
according to specification.
Conformance
This section is
normative.
This section lists requirements for
conformance to WCAG 2.0. It also gives information about
how to make conformance claims, which are optional. Finally,
it describes what it means to be
accessibility supported, since only
accessibility-supported ways of using technologies can be
relied upon for conformance.
Understanding Conformance includes further explanation
of the accessibility-supported concept.
Conformance Requirements
In order for a Web page to conform to WCAG 2.0, all
of the following conformance requirements must be
satisfied:
1.
Conformance Level: One of the following
levels of conformance is met in full.
-
Level A:
For Level A conformance (the minimum level of
conformance), the
Web page
satisfies all the Level A Success Criteria,
or a
conforming alternate version is provided.
-
Level AA:
For Level AA conformance, the Web page satisfies
all the Level A and Level AA Success Criteria,
or a Level AA conforming alternate version is
provided.
-
Level AAA:
For Level AAA conformance, the Web page
satisfies all the Level A, Level AA and Level
AAA Success Criteria, or a Level AAA conforming
alternate version is provided.
Note 1: Although
conformance can only be achieved at the stated
levels, authors are encouraged to report (in
their claim) any progress toward meeting success
criteria from all levels beyond the achieved
level of conformance.
Note 2: It is not
recommended that Level AAA conformance be
required as a general policy for entire sites
because it is not possible to satisfy all Level
AAA Success Criteria for some content.
2. Full
pages:
Conformance (and conformance level) is for full
Web page(s) only, and cannot be achieved if part
of a Web page is excluded.
Note 1: For the
purpose of determining conformance, alternatives
to part of a page's content are considered part
of the page when the alternatives can be
obtained directly from the page, e.g., a long
description or an alternative presentation of a
video.
Note 2:
Authors of Web pages that cannot conform
due to content outside of the author's control
may consider a
Statement of Partial Conformance.
3.
Complete processes: When a
Web page is one of a series of Web pages
presenting a
process (i.e., a sequence of steps that need to
be completed in order to accomplish an activity),
all Web pages in the process conform at the
specified level or better. (Conformance is not
possible at a particular level if any page in the
process does not conform at that level or better.)
Example: An online
store has a series of pages that are used to
select and purchase products. All pages in the
series from start to finish (checkout) conform
in order for any page that is part of the
process to conform.
5.
Non-Interference: If
technologies are used in a way that is not
accessibility supported, or if they are used in
a non-conforming way, then they do not block the
ability of users to access the rest of the page. In
addition, the
Web page as a whole continues to meet the
conformance requirements under each of the following
conditions:
-
when any technology that is not
relied upon is turned on in a user agent,
-
when any technology that is not relied upon
is turned off in a user agent, and
-
when any technology that is not relied upon
is not supported by a user agent
In addition, the following
success criteria apply to all content on the page,
including content that is not otherwise relied upon
to meet conformance, because failure to meet them
could interfere with any use of the page:
-
1.4.2 - Audio Control,
-
2.1.2 - No Keyboard Trap,
-
2.3.1 - Three Flashes or Below
Threshold, and
-
2.2.2 - Pause, Stop, Hide.
Note: If a page
cannot conform (for example, a conformance test
page or an example page), it cannot be included
in the scope of conformance or in a conformance
claim.
For more information, including
examples, see
Understanding Conformance Requirements.
Conformance Claims (Optional)
Conformance is defined only for
Web pages. However, a conformance claim may be made
to cover one page, a series of pages, or multiple
related Web pages.
Required Components of a Conformance Claim
Conformance claims are
not required. Authors can conform to WCAG
2.0 without making a claim. However, if a
conformance claim is made, then the conformance
claim must include the following
information:
-
Date of the claim
-
Guidelines title, version and URI
"Web Content Accessibility Guidelines
2.0 at
http://www.w3.org/TR/2008/REC-WCAG20-20081211/"
-
Conformance level satisfied:
(Level A, AA or AAA)
-
A concise description of the Web
pages, such as a list of URIs for which
the claim is made, including whether subdomains
are included in the claim.
Note 1: The Web
pages may be described by list or by an
expression that describes all of the URIs
included in the claim.
Note 2:
Web-based products that do not have a URI
prior to installation on the customer's Web
site may have a statement that the product
would conform when installed.
-
A list of the
Web content technologies
relied upon.
Note: If a
conformance logo is used, it would constitute a
claim and must be accompanied by the required
components of a conformance claim listed above.
Optional Components of a Conformance Claim
In addition to the required
components of a conformance claim above, consider
providing additional information to assist users.
Recommended additional information includes:
-
A list of success criteria beyond the level
of conformance claimed that have been met. This
information should be provided in a form that
users can use, preferably machine-readable
metadata.
-
A list of the specific technologies that are
"used but not
relied upon."
-
A list of user agents, including assistive
technologies that were used to test the content.
-
Information about any additional steps taken
that go beyond the success criteria to enhance
accessibility.
-
A machine-readable metadata version of the
list of specific technologies that are
relied upon.
-
A machine-readable metadata version of the
conformance claim.
Statement of Partial Conformance - Third Party
Content
Sometimes, Web pages are created that will later have
additional content added to them. For example, an email
program, a blog, an article that allows users to add
comments, or applications supporting user-contributed
content. Another example would be a page, such as a
portal or news site, composed of content aggregated from
multiple contributors, or sites that automatically
insert content from other sources over time, such as
when advertisements are inserted dynamically.
In these cases, it is not possible to
know at the time of original posting what the
uncontrolled content of the pages will be. It is
important to note that the uncontrolled content can
affect the accessibility of the controlled content as
well. Two options are available:
-
A determination of conformance can be made based
on best knowledge. If a page of this type is
monitored and repaired (non-conforming content is
removed or brought into conformance) within two
business days, then a determination or claim of
conformance can be made since, except for errors in
externally contributed content which are corrected
or removed when encountered, the page conforms. No
conformance claim can be made if it is not possible
to monitor or correct non-conforming content;
OR
-
A "statement of partial conformance" may be made
that the page does not conform, but could conform if
certain parts were removed. The form of that
statement would be, "This page does not conform, but
would conform to WCAG 2.0 at level X if the
following parts from uncontrolled sources were
removed." In addition, the following would also be
true of uncontrolled content that is described in
the statement of partial conformance:
-
It is not content that is under the author's
control.
-
It is described in a way that users can
identify (e.g., they cannot be described as "all
parts that we do not control" unless they are
clearly marked as such.)
Statement of Partial Conformance - Language
A "statement of partial conformance due to language"
may be made when the page does not conform, but would
conform if
accessibility support existed for (all of) the
language(s) used on the page. The form of that statement
would be, "This page does not conform, but
would conform to WCAG 2.0 at level X if accessibility
support existed for the following language(s):"
Appendix A:
Glossary
This section is
normative.
-
abbreviation
-
shortened form of a word, phrase, or name where the
abbreviation has not become part of the language
Note 1: This includes
initialisms and acronyms where:
-
initialisms are shortened
forms of a name or phrase made from the initial
letters of words or syllables contained in that
name or phrase
Note 1: Not
defined in all languages.
Example 1: SNCF
is a French initialism that contains the
initial letters of the
Société Nationale des Chemins de Fer,
the French national railroad.
Example 2: ESP
is an initialism for extrasensory
perception.
-
acronyms are abbreviated
forms made from the initial letters or parts of
other words (in a name or phrase) which may be
pronounced as a word
Example: NOAA is
an acronym made from the initial letters of
the National Oceanic and Atmospheric
Administration in the United States.
Note 2: Some companies
have adopted what used to be an initialism as their
company name. In these cases, the new name of the
company is the letters (for example, Ecma) and the
word is no longer considered an abbreviation.
-
accessibility supported
-
supported by users'
assistive technologies as well as the accessibility
features in browsers and other
user agents
To qualify as an accessibility-supported use of a Web
content technology (or feature of a technology), both 1
and 2 must be satisfied for a Web content technology (or
feature):
-
The way that the
Web content technology is used must be supported
by users' assistive technology (AT). This
means that the way that the technology is used has
been tested for interoperability with users'
assistive technology in the
human language(s) of the content,
AND
-
The Web content technology must have
accessibility-supported user agents that are
available to users. This means that at
least one of the following four statements is true:
-
The technology is supported natively in
widely-distributed user agents that are also
accessibility supported (such as HTML and CSS);
OR
-
The technology is supported in a
widely-distributed plug-in that is also
accessibility supported;
OR
-
The content is available in a closed
environment, such as a university or corporate
network, where the user agent required by the
technology and used by the organization is also
accessibility supported;
OR
-
The user agent(s) that support the technology
are accessibility supported and are available
for download or purchase in a way that:
Note 1: The WCAG Working
group and the W3C do not specify which or how much
support by assistive technologies there must be for
a particular use of a Web technology in order for it
to be classified as accessibility supported. (See
Level of Assistive Technology Support Needed for
"Accessibility Support".)
Note 2: Web technologies
can be used in ways that are not accessibility
supported as long as they are not
relied upon and the page as a whole meets the
conformance requirements, including
Conformance Requirement 4: Only
Accessibility-Supported Ways of Using Technologies
and
Conformance Requirement 5: Non-Interference, are
met.
Note 3: When a
Web Technology is used in a way that is
"accessibility supported," it does not imply that
the entire technology or all uses of the technology
are supported. Most technologies, including HTML,
lack support for at least one feature or use. Pages
conform to WCAG only if the uses of the technology
that are accessibility supported can be relied upon
to meet WCAG requirements.
Note 4: When citing Web
content technologies that have multiple versions,
the version(s) supported should be specified.
Note 5: One way for
authors to locate uses of a technology that are
accessibility supported would be to consult
compilations of uses that are documented to be
accessibility supported. (See
Understanding Accessibility-Supported Web Technology
Uses.) Authors, companies, technology vendors,
or others may document accessibility-supported ways
of using Web content technologies. However, all ways
of using technologies in the documentation would
need to meet the definition of
accessibility-supported Web content technologies
above.
-
alternative for time-based media
-
document including correctly sequenced text
descriptions of time-based visual and auditory
information and providing a means for achieving the
outcomes of any time-based interaction
Note: A screenplay used
to create the synchronized media content would meet
this definition only if it was corrected to
accurately represent the final synchronized media
after editing.
-
ambiguous to users in general
-
the purpose cannot be determined from the link and
all information of the Web page presented to the user
simultaneously with the link (i.e., readers without
disabilities would not know what a link would do until
they activated it)
Example: The word guava
in the following sentence "One of the notable
exports is guava" is a link. The link could lead to
a definition of guava, a chart listing the quantity
of guava exported or a photograph of people
harvesting guava. Until the link is activated, all
readers are unsure and the person with a disability
is not at any disadvantage.
-
ASCII art
-
picture created by a spatial arrangement of
characters or glyphs (typically from the 95 printable
characters defined by ASCII).
-
assistive technology (as used in this document)
-
hardware and/or software that acts as a
user agent, or along with a mainstream user agent,
to provide functionality to meet the requirements of
users with disabilities that go beyond those offered by
mainstream user agents
Note 1: functionality
provided by assistive technology includes
alternative presentations (e.g., as synthesized
speech or magnified content), alternative input
methods (e.g., voice), additional navigation or
orientation mechanisms, and content transformations
(e.g., to make tables more accessible).
Note 2: Assistive
technologies often communicate data and messages
with mainstream user agents by using and monitoring
APIs.
Note 3: The distinction
between mainstream user agents and assistive
technologies is not absolute. Many mainstream user
agents provide some features to assist individuals
with disabilities. The basic difference is that
mainstream user agents target broad and diverse
audiences that usually include people with and
without disabilities. Assistive technologies target
narrowly defined populations of users with specific
disabilities. The assistance provided by an
assistive technology is more specific and
appropriate to the needs of its target users. The
mainstream user agent may provide important
functionality to assistive technologies like
retrieving Web content from program objects or
parsing markup into identifiable bundles.
Example: Assistive
technologies that are important in the context of
this document include the following:
-
screen magnifiers, and other visual reading
assistants, which are used by people with
visual, perceptual and physical print
disabilities to change text font, size, spacing,
color, synchronization with speech, etc. in
order to improve the visual readability of
rendered text and images;
-
screen readers, which are used by people who
are blind to read textual information through
synthesized speech or braille;
-
text-to-speech software, which is used by
some people with cognitive, language, and
learning disabilities to convert text into
synthetic speech;
-
speech recognition software, which may be
used by people who have some physical
disabilities;
-
alternative keyboards, which are used by
people with certain physical disabilities to
simulate the keyboard (including alternate
keyboards that use head pointers, single
switches, sip/puff and other special input
devices.);
-
alternative pointing devices, which are used
by people with certain physical disabilities to
simulate mouse pointing and button activations.
-
audio
-
the technology of sound reproduction
Note: Audio can be
created synthetically (including speech synthesis),
recorded from real world sounds, or both.
-
audio
description
-
narration added to the soundtrack to describe
important visual details that cannot be understood from
the main soundtrack alone
Note 1: Audio
description of
video provides information about actions,
characters, scene changes, on-screen text, and other
visual content.
Note 2: In standard
audio description, narration is added during
existing pauses in dialogue. (See also
extended audio description.)
Note 3: Where all of the
video information is already provided in
existing
audio, no additional audio description is
necessary.
Note 4: Also called
"video description" and "descriptive narration."
-
audio-only
-
a time-based presentation that contains only
audio (no
video and no interaction)
-
blinking
-
switch back and forth between two visual states in a
way that is meant to draw attention
Note: See also
flash. It is possible for something to be large
enough and blink brightly enough at the right
frequency to be also classified as a flash.
-
blocks of
text
-
more than one sentence of text
-
CAPTCHA
-
initialism for "Completely Automated Public Turing
test to tell Computers and Humans Apart"
Note 1: CAPTCHA tests
often involve asking the user to type in text that
is displayed in an obscured image or audio file.
Note 2: A Turing test is
any system of tests designed to differentiate a
human from a computer. It is named after famed
computer scientist Alan Turing. The term was coined
by researchers at Carnegie Mellon University.
[CAPTCHA]
-
captions
-
synchronized visual and/or
text alternative for both speech and non-speech
audio information needed to understand the media content
Note 1: Captions are
similar to dialogue-only subtitles except captions
convey not only the content of spoken dialogue, but
also equivalents for non-dialogue audio information
needed to understand the program content, including
sound effects, music, laughter, speaker
identification and location.
Note 2: Closed Captions
are equivalents that can be turned on and off with
some players.
Note 3: Open Captions
are any captions that cannot be turned off. For
example, if the captions are visual equivalent
images of text embedded in
video.
Note 4: Captions should
not obscure or obstruct relevant information in the
video.
Note 5: In some
countries, captions are called subtitles.
Note 6:
Audio descriptions can be, but do not need to
be, captioned since they are descriptions of
information that is already presented visually.
-
changes of context
-
major changes in the content of the
Web page that, if made without user awareness, can
disorient users who are not able to view the entire page
simultaneously
Changes in context include changes of:
-
user agent;
-
viewport;
-
focus;
-
content that changes the meaning of the
Web page.
Note: A change of
content is not always a change of context. Changes
in content, such as an expanding outline, dynamic
menu, or a tab control do not necessarily change the
context, unless they also change one of the above
(e.g., focus).
Example: Opening a new
window, moving focus to a different component, going
to a new page (including anything that would look to
a user as if they had moved to a new page) or
significantly re-arranging the content of a page are
examples of changes of context.
-
conformance
-
satisfying all the requirements of a given standard,
guideline or specification
-
conforming alternate version
-
version that
-
conforms at the designated level, and
-
provides all of the same information and
functionality in the same
human language, and
-
is as up to date as the non-conforming content,
and
-
for which at least one of the following is true:
-
the conforming version can be reached from
the non-conforming page via an
accessibility-supported
mechanism, or
-
the non-conforming version can only be
reached from the conforming version, or
-
the non-conforming version can only be
reached from a conforming page that also
provides a mechanism to reach the conforming
version
Note 1: In this
definition, "can only be reached" means that there
is some mechanism, such as a conditional redirect,
that prevents a user from "reaching" (loading) the
non-conforming page unless the user had just come
from the conforming version.
Note 2: The alternate
version does not need to be matched page for page
with the original (e.g., the conforming alternate
version may consist of multiple pages).
Note 3: If multiple
language versions are available, then conforming
alternate versions are required for each language
offered.
Note 4: Alternate
versions may be provided to accommodate different
technology environments or user groups. Each version
should be as conformant as possible. One version
would need to be fully conformant in order to meet
conformance requirement 1.
Note 5: The conforming
alternative version does not need to reside within
the scope of conformance, or even on the same Web
site, as long as it is as freely available as the
non-conforming version.
Note 6: Alternate
versions should not be confused with
supplementary content, which support the
original page and enhance comprehension.
Note 7: Setting user
preferences within the content to produce a
conforming version is an acceptable mechanism for
reaching another version as long as the method used
to set the preferences is accessibility supported.
See
Understanding Conforming Alternate Versions
-
content (Web content)
-
information and sensory experience to be communicated
to the user by means of a
user agent, including code or markup that defines
the content's
structure,
presentation, and interactions
-
context-sensitive help
-
help text that provides information related to the
function currently being performed
Note: Clear labels can
act as context-sensitive help.
-
contrast ratio
-
(L1 + 0.05) / (L2 + 0.05), where
Note 1: Contrast ratios
can range from 1 to 21 (commonly written 1:1 to
21:1).
Note 2: Because authors
do not have control over user settings as to how
text is rendered (for example font smoothing or
anti-aliasing), the contrast ratio for text can be
evaluated with anti-aliasing turned off.
Note 3: For the purpose
of Success Criteria 1.4.3 and 1.4.6, contrast is
measured with respect to the specified background
over which the text is rendered in normal usage. If
no background color is specified, then white is
assumed.
Note 4: Background color
is the specified color of content over which the
text is to be rendered in normal usage. It is a
failure if no background color is specified when the
text color is specified, because the user's default
background color is unknown and cannot be evaluated
for sufficient contrast. For the same reason, it is
a failure if no text color is specified when a
background color is specified.
Note 5: When there is a
border around the letter, the border can add
contrast and would be used in calculating the
contrast between the letter and its background. A
narrow border around the letter would be used as the
letter. A wide border around the letter that fills
in the inner details of the letters acts as a halo
and would be considered background.
Note 6: WCAG conformance
should be evaluated for color pairs specified in the
content that an author would expect to appear
adjacent in typical presentation. Authors need not
consider unusual presentations, such as color
changes made by the user agent, except where caused
by authors' code.
-
correct reading sequence
-
any sequence where words and paragraphs are presented
in an order that does not change the meaning of the
content
-
emergency
-
a sudden, unexpected situation or occurrence that
requires immediate action to preserve health, safety, or
property
-
essential
-
if removed, would fundamentally change the
information or functionality of the content, and
information and functionality cannot be achieved in
another way that would conform
-
extended audio description
-
audio description that is added to an audiovisual
presentation by pausing the
video so that there is time to add additional
description
Note: This technique is
only used when the sense of the
video would be lost without the additional
audio description and the pauses between
dialogue/narration are too short.
-
flash
-
a pair of opposing changes in
relative luminance that can cause seizures in some
people if it is large enough and in the right frequency
range
-
functionality
-
processes and outcomes achievable through user
action
-
general flash and red flash thresholds
-
a
flash or rapidly changing image sequence is below
the threshold (i.e., content passes) if
any of the following are true:
-
there are no more than three general
flashes and / or no more than three
red flashes within any one-second period;
or
-
the combined area of flashes occurring
concurrently occupies no more than a total of .006
steradians within any 10 degree visual field on the
screen (25% of any 10 degree visual field on the
screen) at typical viewing distance
where:
-
A general flash is defined as a
pair of opposing changes in
relative luminance of 10% or more of the maximum
relative luminance where the relative luminance of
the darker image is below 0.80; and where "a pair of
opposing changes" is an increase followed by a
decrease, or a decrease followed by an increase, and
-
A red flash is defined as any
pair of opposing transitions involving a saturated
red.
Exception: Flashing that is a fine,
balanced, pattern such as white noise or an alternating
checkerboard pattern with "squares" smaller than 0.1
degree (of visual field at typical viewing distance) on
a side does not violate the thresholds.
Note 1: For general
software or Web content, using a 341 x 256 pixel
rectangle anywhere on the displayed screen area when
the content is viewed at 1024 x 768 pixels will
provide a good estimate of a 10 degree visual field
for standard screen sizes and viewing distances
(e.g., 15-17 inch screen at 22-26 inches). (Higher
resolutions displays showing the same rendering of
the content yield smaller and safer images so it is
lower resolutions that are used to define the
thresholds.)
Note 2: A transition is
the change in relative luminance (or relative
luminance/color for red flashing) between adjacent
peaks and valleys in a plot of relative luminance
(or relative luminance/color for red flashing)
measurement against time. A flash consists of two
opposing transitions.
Note 3: The current
working definition in the field for "pair of
opposing transitions involving a saturated red"
is where, for either or both states involved in each
transition, R/(R+ G + B) >= 0.8, and the change in
the value of (R-G-B)x320 is > 20 (negative values of
(R-G-B)x320 are set to zero) for both transitions.
R, G, B values range from 0-1 as specified in
“relative luminance” definition.
[HARDING-BINNIE]
Note 4: Tools are
available that will carry out analysis from video
screen capture. However, no tool is necessary to
evaluate for this condition if flashing is less than
or equal to 3 flashes in any one second. Content
automatically passes (see #1 and #2 above).
-
human
language
-
language that is spoken, written or signed (through
visual or tactile means) to communicate with humans
-
idiom
-
phrase whose meaning cannot be deduced from the
meaning of the individual words and the specific words
cannot be changed without losing the meaning
Note: idioms cannot be
translated directly, word for word, without losing
their (cultural or language-dependent) meaning.
Example 1: In English,
"spilling the beans" means "revealing a secret."
However, "knocking over the beans" or "spilling the
vegetables" does not mean the same thing.
Example 2: In Japanese,
the phrase "さじを投げる"
literally translates into "he throws a spoon," but
it means that there is nothing he can do and finally
he gives up.
Example 3: In Dutch, "Hij
ging met de kippen op stok" literally
translates into "He went to roost with the
chickens," but it means that he went to bed early.
-
image of text
-
text that has been rendered in a non-text form (e.g.,
an image) in order to achieve a particular visual effect
Note: This does not
include
text that is part of a picture that contains
significant other visual content.
Example: A person's name
on a nametag in a photograph.
-
informative
-
for information purposes and not required for
conformance
-
input
error
-
information provided by the user that is not accepted
Note: This includes:
-
Information that is required by the
Web page but omitted by the user
-
Information that is provided by the user but
that falls outside the required data format or
values
-
jargon
-
words used in a particular way by people in a
particular field
Example: The word
StickyKeys is jargon from the field of assistive
technology/accessibility.
-
keyboard interface
-
interface used by software to obtain keystroke input
Note 1: A keyboard
interface allows users to provide keystroke input to
programs even if the native technology does not
contain a keyboard.
Example: A
touchscreen PDA has a keyboard interface built
into its operating system as well as a connector
for external keyboards. Applications on the PDA
can use the interface to obtain keyboard input
either from an external keyboard or from other
applications that provide simulated keyboard
output, such as handwriting interpreters or
speech-to-text applications with "keyboard
emulation" functionality.
Note 2: Operation of the
application (or parts of the application) through a
keyboard-operated mouse emulator, such as MouseKeys,
does not qualify as operation through a keyboard
interface because operation of the program is
through its pointing device interface, not through
its keyboard interface.
-
label
-
text or other component with a
text alternative that is presented to a user to
identify a component within Web
content
Note 1: A label is
presented to all users whereas the
name may be hidden and only exposed by assistive
technology. In many (but not all) cases the name and
the label are the same.
Note 2: The term label
is not limited to the label element in HTML.
-
large
scale (text)
-
with at least 18 point or 14 point bold or font size
that would yield equivalent size for Chinese, Japanese
and Korean (CJK) fonts
Note 1: Fonts with
extraordinarily thin strokes or unusual features and
characteristics that reduce the familiarity of their
letter forms are harder to read, especially at lower
contrast levels.
Note 2: Font size is the
size when the content is delivered. It does not
include resizing that may be done by a user.
Note 3: The actual size
of the character that a user sees is dependent both
on the author-defined size and the user's display or
user-agent settings. For many mainstream body text
fonts, 14 and 18 point is roughly equivalent to 1.2
and 1.5 em or to 120% or 150% of the default size
for body text (assuming that the body font is 100%),
but authors would need to check this for the
particular fonts in use. When fonts are defined in
relative units, the actual point size is calculated
by the user agent for display. The point size should
be obtained from the user agent, or calculated based
on font metrics as the user agent does, when
evaluating this success criterion. Users who have
low vision would be responsible for choosing
appropriate settings.
Note 4: When using text
without specifying the font size, the smallest font
size used on major browsers for unspecified text
would be a reasonable size to assume for the font.
If a level 1 heading is rendered in 14pt bold or
higher on major browsers, then it would be
reasonable to assume it is large text. Relative
scaling can be calculated from the default sizes in
a similar fashion.
Note 5: The 18 and 14
point sizes for roman texts are taken from the
minimum size for large print (14pt) and the larger
standard font size (18pt). For other fonts such as
CJK languages, the "equivalent" sizes would be the
minimum large print size used for those languages
and the next larger standard large print size.
-
legal commitments
-
transactions where the person incurs a legally
binding obligation or benefit
Example: A marriage
license, a stock trade (financial and legal), a
will, a loan, adoption, signing up for the army, a
contract of any type, etc.
-
link
purpose
-
nature of the result obtained by activating a
hyperlink
-
live
-
information captured from a real-world event and
transmitted to the receiver with no more than a
broadcast delay
Note 1: A broadcast
delay is a short (usually automated) delay, for
example used in order to give the broadcaster time
to queue or censor the audio (or video) feed, but
not sufficient to allow significant editing.
Note 2: If information
is completely computer generated, it is not live.
-
lower
secondary education level
-
the two or three year period of education that begins
after completion of six years of school and ends nine
years after the beginning of
primary education
Note: This definition is
based on the International Standard Classification
of Education
[UNESCO].
-
mechanism
-
process or technique for achieving a result
Note 1: The mechanism
may be explicitly provided in the content, or may be
relied upon to be provided by either the
platform or by
user agents, including
assistive technologies.
Note 2: The mechanism
needs to meet all success criteria for the
conformance level claimed.
-
media alternative for text
-
media that presents no more information than is
already presented in text (directly or via text
alternatives)
Note: A media
alternative for text is provided for those who
benefit from alternate representations of text.
Media alternatives for text may be audio-only,
video-only (including sign-language video), or
audio-video.
-
name
-
text by which software can identify a component
within Web content to the user
Note 1: The name may be
hidden and only exposed by assistive technology,
whereas a
label is presented to all users. In many (but
not all) cases, the label and the name are the same.
Note 2: This is
unrelated to the name attribute in HTML.
-
navigated sequentially
-
navigated in the order defined for advancing focus
(from one element to the next) using a
keyboard interface
-
non-text content
-
any content that is not a sequence of characters that
can be
programmatically determined or where the sequence is
not expressing something in
human language
Note: This includes
ASCII Art (which is a pattern of characters),
emoticons, leetspeak (which uses character
substitution), and images representing text
-
normative
-
required for conformance
Note 1: One may conform
in a variety of well-defined ways to this document.
Note 2: Content
identified as "informative"
or "non-normative" is never required for
conformance.
-
on a full-screen window
-
on the most common sized desktop/laptop display with
the viewport maximized
Note: Since people
generally keep their computers for several years, it
is best not to rely on the latest desktop/laptop
display resolutions but to consider the common
desktop/laptop display resolutions over the course
of several years when making this evaluation.
-
paused
-
stopped by user request and not resumed until
requested by user
-
prerecorded
-
information that is not
live
-
presentation
-
rendering of the
content in a form to be perceived by users
-
primary
education level
-
six year time period that begins between the ages of
five and seven, possibly without any previous education
Note: This definition is
based on the International Standard Classification
of Education
[UNESCO].
-
process
-
series of user actions where each action is required
in order to complete an activity
Example 1: Successful
use of a series of Web pages on a shopping site
requires users to view alternative products, prices
and offers, select products, submit an order,
provide shipping information and provide payment
information.
Example 2: An account
registration page requires successful completion of
a Turing test before the registration form can be
accessed.
-
programmatically determined (programmatically
determinable)
-
determined by software from author-supplied data
provided in a way that different
user agents, including
assistive technologies, can extract and present this
information to users in different modalities
Example 1: Determined in
a markup language from elements and attributes that
are accessed directly by commonly available
assistive technology.
Example 2: Determined
from technology-specific data structures in a
non-markup language and exposed to assistive
technology via an accessibility
API that is supported by commonly
available assistive technology.
-
programmatically determined link context
-
additional information that can be
programmatically determined from
relationships with a link, combined with the link
text, and presented to users in different modalities
Example: In HTML,
information that is programmatically determinable
from a link in English includes text that is in the
same paragraph, list, or table cell as the link or
in a table header cell that is associated with the
table cell that contains the link.
Note: Since screen
readers interpret punctuation, they can also provide
the context from the current sentence, when the
focus is on a link in that sentence.
-
programmatically set
-
set by software using methods that are supported by
user agents, including assistive technologies
-
pure decoration
-
serving only an aesthetic purpose, providing no
information, and having no functionality
Note: Text is only
purely decorative if the words can be rearranged or
substituted without changing their purpose.
Example: The cover page
of a dictionary has random words in very light text
in the background.
-
real-time event
-
event that a) occurs at the same time as the viewing
and b) is not completely generated by the content
Example 1: A Webcast of
a live performance (occurs at the same time as the
viewing and is not prerecorded).
Example 2: An on-line
auction with people bidding (occurs at the same time
as the viewing).
Example 3: Live humans
interacting in a virtual world using avatars (is not
completely generated by the content and occurs at
the same time as the viewing).
-
relationships
-
meaningful associations between distinct pieces of
content
-
relative luminance
-
the relative brightness of any point in a colorspace,
normalized to 0 for darkest black and 1 for lightest
white
Note 1: For the sRGB
colorspace, the relative luminance of a color is
defined as L = 0.2126 * R + 0.7152
* G + 0.0722 * B
where R, G and
B are defined as:
-
if RsRGB <= 0.03928 then R
= RsRGB/12.92 else R
= ((RsRGB+0.055)/1.055) ^ 2.4
-
if GsRGB <= 0.03928 then G
= GsRGB/12.92 else G
= ((GsRGB+0.055)/1.055) ^ 2.4
-
if BsRGB <= 0.03928 then B
= BsRGB/12.92 else B
= ((BsRGB+0.055)/1.055) ^ 2.4
and RsRGB, GsRGB,
and BsRGB are defined as:
-
RsRGB = R8bit/255
-
GsRGB = G8bit/255
-
BsRGB = B8bit/255
The "^" character is the
exponentiation operator. (Formula taken from
[sRGB] and
[IEC-4WD]).
Note 2: Almost all
systems used today to view Web content assume sRGB
encoding. Unless it is known that another color
space will be used to process and display the
content, authors should evaluate using sRGB
colorspace. If using other color spaces, see
Understanding Success Criterion 1.4.3.
Note 3: If dithering
occurs after delivery, then the source color value
is used. For colors that are dithered at the source,
the average values of the colors that are dithered
should be used (average R, average G, and average
B).
Note 4: Tools are
available that automatically do the calculations
when testing contrast and flash.
Note 5: A
MathML version of the relative luminance definition
is available.
-
relied
upon (technologies that are)
-
the content would not
conform if that
technology is turned off or is not supported
-
role
-
text or number by which software can identify the
function of a component within Web content
Example: A number that
indicates whether an image functions as a hyperlink,
command button, or check box.
-
same functionality
-
same result when used
Example: A submit
"search" button on one Web page and a "find" button
on another Web page may both have a field to enter a
term and list topics in the Web site related to the
term submitted. In this case, they would have the
same functionality but would not be labeled
consistently.
-
same
relative order
-
same position relative to other items
Note: Items are
considered to be in the same relative order even if
other items are inserted or removed from the
original order. For example, expanding navigation
menus may insert an additional level of detail or a
secondary navigation section may be inserted into
the reading order.
-
satisfies a
success criterion
-
the success criterion does not evaluate to 'false'
when applied to the page
-
section
-
A self-contained portion of written content that
deals with one or more related topics or thoughts
Note: A section may
consist of one or more paragraphs and include
graphics, tables, lists and sub-sections.
-
set of Web pages
-
collection of
Web pages that share a common purpose and that are
created by the same author, group or organization
Note: Different language
versions would be considered different sets of Web
pages.
-
sign language
-
a language using combinations of movements of the
hands and arms, facial expressions, or body positions to
convey meaning
-
sign language interpretation
-
translation of one language, generally a spoken
language, into a
sign language
Note: True sign
languages are independent languages that are
unrelated to the spoken language(s) of the same
country or region.
-
specific
sensory experience
-
a sensory experience that is not purely decorative
and does not primarily convey important information or
perform a function
Example: Examples
include a performance of a flute solo, works of
visual art etc.
-
structure
-
-
The way the parts of a
Web page are organized in relation to each
other; and
-
The way a collection of
Web pages is organized
-
supplemental content
-
additional
content that illustrates or clarifies the primary
content
Example 1: An audio
version of a
Web page.
Example 2: An
illustration of a complex
process.
Example 3: A paragraph
summarizing the major outcomes and recommendations
made in a research study.
-
synchronized media
-
audio or
video synchronized with another format for
presenting information and/or with time-based
interactive components, unless the media is a
media alternative for text that is clearly labeled
as such
-
technology (Web content)
-
mechanism for encoding instructions to be rendered,
played or executed by
user agents
Note 1: As used in these
guidelines "Web Technology" and the word
"technology" (when used alone) both refer to Web
Content Technologies.
Note 2: Web content
technologies may include markup languages, data
formats, or programming languages that authors may
use alone or in combination to create end-user
experiences that range from static Web pages to
synchronized media presentations to dynamic Web
applications.
Example: Some common
examples of Web content technologies include
HTML,
CSS,
SVG,
PNG,
PDF,
Flash, and JavaScript.
-
text
-
sequence of characters that can be
programmatically determined, where the sequence is
expressing something in
human language
-
text
alternative
-
Text that is programmatically associated with
non-text content or referred to from text that is
programmatically associated with non-text content.
Programmatically associated text is text whose location
can be programmatically determined from the non-text
content.
Example: An image of a
chart is described in text in the paragraph after
the chart. The short text alternative for the chart
indicates that a description follows.
-
used in an unusual or restricted way
-
words used in such a way that requires users to know
exactly which definition to apply in order to understand
the content correctly
Example: The term "gig"
means something different if it occurs in a
discussion of music concerts than it does in article
about computer hard drive space, but the appropriate
definition can be determined from context. By
contrast, the word "text" is used in a very specific
way in WCAG 2.0, so a definition is supplied in the
glossary.
-
user agent
-
any software that retrieves and presents Web content
for users
Example: Web browsers,
media players, plug-ins, and other programs —
including
assistive technologies — that help in
retrieving, rendering, and interacting with Web
content.
-
user-controllable
-
data that is intended to be accessed by users
Note: This does not
refer to such things as Internet logs and search
engine monitoring data.
Example: Name and
address fields for a user's account.
-
user interface component
-
a part of the content that is perceived by users as a
single control for a distinct function
Note 1: Multiple user
interface components may be implemented as a single
programmatic element. Components here is not tied to
programming techniques, but rather to what the user
perceives as separate controls.
Note 2: User interface
components include form elements and links as well
as components generated by scripts.
Example: An applet has a
"control" that can be used to move through content
by line or page or random access. Since each of
these would need to have a name and be settable
independently, they would each be a "user interface
component."
-
video
-
the technology of moving or sequenced pictures or
images
Note: Video can be made
up of animated or photographic images, or both.
-
video-only
-
a time-based presentation that contains only
video (no
audio and no interaction)
-
viewport
-
object in which the user agent presents content
Note 1: The
user agent presents content through one or more
viewports. Viewports include windows, frames,
loudspeakers, and virtual magnifying glasses. A
viewport may contain another viewport (e.g., nested
frames). Interface components created by the user
agent such as prompts, menus, and alerts are not
viewports.
Note 2: This definition
is based on
User Agent Accessibility Guidelines 1.0 Glossary.
-
visually customized
-
the font, size, color, and background can be set
-
Web page
-
a non-embedded resource obtained from a single URI
using HTTP plus any other resources that are used in the
rendering or intended to be rendered together with it by
a
user agent
Note 1: Although any
"other resources" would be rendered together with
the primary resource, they would not necessarily be
rendered simultaneously with each other.
Note 2: For the purposes
of conformance with these guidelines, a resource
must be "non-embedded" within the scope of
conformance to be considered a Web page.
Example 1: A Web
resource including all embedded images and media.
Example 2: A Web mail
program built using Asynchronous JavaScript and XML
(AJAX). The program lives entirely at
http://example.com/mail, but includes an inbox, a
contacts area and a calendar. Links or buttons are
provided that cause the inbox, contacts, or calendar
to display, but do not change the URI of the page as
a whole.
Example 3: A
customizable portal site, where users can choose
content to display from a set of different content
modules.
Example 4: When you
enter "http://shopping.example.com/" in your
browser, you enter a movie-like interactive shopping
environment where you visually move around in a
store dragging products off of the shelves around
you and into a visual shopping cart in front of you.
Clicking on a product causes it to be demonstrated
with a specification sheet floating alongside. This
might be a single-page Web site or just one page
within a Web site.
Appendix B: Acknowledgments
This section is
informative.
This publication has been funded in part with Federal
funds from the U.S. Department of Education, National
Institute on Disability and Rehabilitation Research (NIDRR)
under contract number ED05CO0039. The content of this
publication does not necessarily reflect the views or
policies of the U.S. Department of Education, nor does
mention of trade names, commercial products, or
organizations imply endorsement by the U.S. Government.
Additional information about participation in the Web
Content Accessibility Guidelines Working Group (WCAG WG) can
be found on the Working
Group home page.
Participants
active in the WCAG WG at the time of publication
-
Bruce Bailey (U.S. Access Board)
-
Frederick Boland (NIST)
-
Ben Caldwell (Trace R&D Center, University of
Wisconsin)
-
Sofia Celic (W3C Invited Expert)
-
Michael Cooper (W3C)
-
Roberto Ellero (International Webmasters
Association / HTML Writers Guild)
-
Bengt Farre (Rigab)
-
Loretta Guarino Reid (Google)
-
Katie Haritos-Shea
-
Andrew Kirkpatrick (Adobe)
-
Drew LaHart (IBM)
-
Alex Li (SAP AG)
-
David MacDonald (E-Ramp Inc.)
-
Roberto Scano (International Webmasters
Association / HTML Writers Guild)
-
Cynthia Shelly (Microsoft)
-
Andi Snow-Weaver (IBM)
-
Christophe Strobbe (DocArch, K.U.Leuven)
-
Gregg Vanderheiden (Trace R&D Center, University
of Wisconsin)
Other previously
active WCAG WG participants and other contributors to
WCAG 2.0
Shadi Abou-Zahra, Jim Allan, Jenae Andershonis, Avi
Arditti, Aries Arditi, Mike Barta, Sandy Bartell, Kynn
Bartlett, Marco Bertoni, Harvey Bingham, Chris Blouch,
Paul Bohman, Patrice Bourlon, Judy Brewer, Andy Brown,
Dick Brown, Doyle Burnett, Raven Calais, Tomas Caspers,
Roberto Castaldo, Sambhavi Chandrashekar, Mike Cherim,
Jonathan Chetwynd, Wendy Chisholm, Alan Chuter, David M
Clark, Joe Clark, James Coltham, James Craig, Tom
Croucher, Nir Dagan, Daniel Dardailler, Geoff Deering,
Pete DeVasto, Don Evans, Neal Ewers, Steve Faulkner,
Lainey Feingold, Alan J. Flavell, Nikolaos Floratos,
Kentarou Fukuda, Miguel Garcia, P.J. Gardner, Greg Gay,
Becky Gibson, Al Gilman, Kerstin Goldsmith, Michael
Grade, Jon Gunderson, Emmanuelle Gutiérrez y Restrepo,
Brian Hardy, Eric Hansen, Sean Hayes, Shawn Henry, Hans
Hillen, Donovan Hipke, Bjoern Hoehrmann, Chris Hofstader,
Yvette Hoitink, Carlos Iglesias, Ian Jacobs, Phill
Jenkins, Jyotsna Kaki, Leonard R. Kasday, Kazuhito
Kidachi, Ken Kipness, Marja-Riitta Koivunen, Preety
Kumar, Gez Lemon, Chuck Letourneau, Scott Luebking, Tim
Lacy, Jim Ley, William Loughborough, Greg Lowney, Luca
Mascaro, Liam McGee, Jens Meiert, Niqui Merret,
Alessandro Miele, Mathew J Mirabella, Charles
McCathieNevile , Matt May, Marti McCuller, Sorcha Moore,
Charles F. Munat, Robert Neff, Bruno von Niman, Tim
Noonan, Sebastiano Nutarelli, Graham Oliver, Sean B.
Palmer, Sailesh Panchang, Nigel Peck, Anne Pemberton,
David Poehlman, Adam Victor Reed, Chris Ridpath, Lee
Roberts, Gregory J. Rosmaita, Matthew Ross, Sharron
Rush, Gian Sampson-Wild, Joel Sanda, Gordon Schantz,
Lisa Seeman, John Slatin, Becky Smith, Jared Smith, Neil
Soiffer, Jeanne Spellman, Mike Squillace, Michael
Stenitzer, Jim Thatcher, Terry Thompson, Justin Thorp,
Makoto Ueki, Eric Velleman, Dena Wainwright, Paul Walsch,
Takayuki Watanabe, Jason White.
Appendix C:
References
This section is
informative.
- CAPTCHA
- The CAPTCHA Project,
Carnegie Mellon University. The project is online at
http://www.captcha.net.
-
HARDING-BINNIE
-
Harding G. F. A. and Binnie, C.D., Independent Analysis
of the ITC Photosensitive Epilepsy Calibration Test
Tape. 2002.
- IEC-4WD
- IEC/4WD 61966-2-1:
Colour Measurement and Management in Multimedia Systems
and Equipment - Part 2.1: Default Colour Space - sRGB.
May 5, 1998.
- sRGB
- "A Standard Default Color
Space for the Internet - sRGB," M. Stokes, M. Anderson,
S. Chandrasekar, R. Motta, eds., Version 1.10, November
5, 1996. A copy of this paper is available at
http://www.w3.org/Graphics/Color/sRGB.html.
- UNESCO
- International Standard
Classification of Education, 1997. A copy of the
standard is available at
http://www.unesco.org/education/information/nfsunesco/doc/isced_1997.htm.
- WCAG10
- Web Content
Accessibility Guidelines 1.0, G. Vanderheiden, W.
Chisholm, I. Jacobs, Editors, W3C Recommendation, 5 May
1999,
http://www.w3.org/TR/1999/WAI-WEBCONTENT-19990505/. The
latest version of WCAG 1.0 is available at
http://www.w3.org/TR/WAI-WEBCONTENT/.
The above from
http://www.w3.org/TR/WCAG20/
Please contact us at
examiner@yennik.com if a link does not work or has changed.
|