Web Content Accessibility Guidelines (WCAG) 2.1

Web Content Accessibility Guidelines (WCAG) 2.1
Web Content Accessibility Guidelines (WCAG) 2.1
W3C
Recommendation
05 June 2018
This version:
Latest published version:
Latest editor's draft:
Implementation report:
Previous version:
Previous Recommendation:
Editors:
Andrew Kirkpatrick
(Adobe)
Joshue O Connor
(Invited Expert, InterAccess)
Alastair Campbell
(Nomensa)
Michael Cooper
W3C
WCAG 2.0 Editors (until December 2008):
Ben Caldwell
(Trace R&D Center, University of Wisconsin-Madison)
Loretta Guarino Reid
(Google, Inc.)
Gregg Vanderheiden
(Trace R&D Center, University of Wisconsin-Madison)
Wendy Chisholm
W3C
John Slatin
(Accessibility Institute, University of Texas at Austin)
Jason White
(University of Melbourne)
Please check the
errata
for any errors or issues
reported since publication.
See also
translations
This document is also available in non-normative formats, available from
Alternate Versions of Web Content Accessibility Guidelines 2.1
2017-2018
W3C
MIT
ERCIM
Keio
Beihang
).
W3C
liability
trademark
and
document use
rules apply.
Abstract
Web Content Accessibility Guidelines (WCAG) 2.1 covers a wide range of recommendations for making Web content more accessible. Following these guidelines will make content more accessible to a wider range of people with disabilities, including accommodations for blindness and low vision, deafness and hearing loss, limited movement, speech disabilities, photosensitivity, and combinations of these, and some accommodation for learning disabilities and cognitive limitations; but will not address every user need for people with these disabilities. These guidelines address accessibility of web content on desktops, laptops, tablets, and mobile devices. Following these guidelines will also often make Web content more usable to users in general.
WCAG 2.1 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 2.1 extends
Web Content Accessibility Guidelines 2.0
WCAG20
], which was published as a
W3C
Recommendation December 2008. Content that conforms to WCAG 2.1 also conforms to WCAG 2.0. The WG intends that for policies requiring conformance to WCAG 2.0, WCAG 2.1 can provide an alternate means of conformance. The publication of WCAG 2.1 does not deprecate or supersede WCAG 2.0. While WCAG 2.0 remains a
W3C
Recommendation, the
W3C
advises the use of WCAG 2.1 to maximize future applicability of accessibility efforts. The
W3C
also encourages use of the most current version of WCAG when developing or updating Web accessibility policies.
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 https://www.w3.org/TR/.
This is a
Recommendation
of WCAG 2.1 by the
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.
By publishing this Recommendation,
W3C
expects the functionality specified in this Recommendation will not be affected by changes to CSS Values and Units Module Level 3 or by Pointer Events Level 2. The Working Group will continue to track these specifications.
To comment,
file an issue in the
W3C
WCAG GitHub repository
. The Working Group requests that public comments be filed as new issues, one issue per discrete comment. It is free to create a GitHub account to file issues. If filing issues in GitHub is not feasible, send email to
public-agwg-comments@w3.org
comment archive
). Comments received on the WCAG 2.1 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. A list of
issues filed
as well as
Archives of the AG WG mailing list discussions
are publicly available, and future work undertaken by the Working Group may address comments received on this document.
This document was published by the
Accessibility Guidelines Working Group
as a Recommendation.
Please see the Working Group's
implementation
report
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.
This document was produced by
a group
operating under the
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
This document is governed by the
1 February 2018
W3C
Process Document
Introduction
This section is non-normative.
0.1
Background on WCAG 2
Web Content Accessibility Guidelines (WCAG) 2.1 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 2.1 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 2.1 builds on WCAG 2.0 [
WCAG20
], which in turn built on WCAG 1.0 [
WAI-WEBCONTENT
] 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
Significant challenges were encountered in defining additional criteria to address cognitive, language, and learning disabilities, including a short timeline for development as well as challenges in reaching consensus on testability, implementability, and international considerations of proposals. Work will carry on in this area in future versions of WCAG. We encourage authors to refer to our supplemental guidance on
improving inclusion for people with disabilities, including learning and cognitive disabilities, people with low-vision, and more
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:
Essential Components of Web Accessibility
User Agent Accessibility Guidelines (UAAG) Overview
Authoring Tool Accessibility Guidelines (ATAG) Overview
0.2
WCAG 2 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 13 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.
0.3
WCAG 2.1 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 2.1
- A customizable quick reference to WCAG 2.1 that includes all of the guidelines, success criteria, and techniques for authors to use as they are developing and evaluating Web content. This includes content from WCAG 2.0 and WCAG 2.1 and can be filtered in many ways to help authors focus on relevant content.
Understanding WCAG 2.1
- A guide to understanding and implementing WCAG 2.1. There is a short "Understanding" document for each guideline and success criterion in WCAG 2.1 as well as key topics.
Techniques for WCAG 2.1
- A collection of techniques and common failures, each in a separate document that includes a description, examples, code and tests.
The WCAG 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. 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
0.4
Requirements for WCAG 2.1
WCAG 2.1 meets a set of
requirements for WCAG 2.1
which, in turn, inherit requirements from WCAG 2.0. Requirements structure the overall framework of guidelines and ensure backwards compatibility. The Working Group also used a less formal set of acceptance criteria for success criteria, to help ensure success criteria are similar in style and quality to those in WCAG 2.0. These requirements constrained what could be included in WCAG 2.1. This constraint was important to preserve its nature as a dot-release of WCAG 2.
0.5
Comparison with WCAG 2.0
WCAG 2.1 was initiated with the goal to improve accessibility guidance for three major groups: users with cognitive or learning disabilities, users with low vision, and users with disabilities on mobile devices. Many ways to meet these needs were proposed and evaluated, and a set of these were refined by the Working Group. Structural requirements inherited from WCAG 2.0, clarity and impact of proposals, and timeline led to the final set of success criteria included in this version. The Working Group considers that WCAG 2.1 incrementally advances web content accessibility guidance for all these areas, but underscores that not all user needs are met by these guidelines.
WCAG 2.1 builds on and is backwards compatible with WCAG 2.0, meaning web pages that conform to WCAG 2.1 also conform to WCAG 2.0. Authors that are required by policy to conform with WCAG 2.0 will be able to update content to WCAG 2.1 without losing conformance with WCAG 2.0. Authors following both sets of guidelines should be aware of the following differences:
0.5.1
New Features in WCAG 2.1
WCAG 2.1 extends WCAG 2.0 by adding new success criteria, definitions to support them, guidelines to organize the additions, and a couple additions to the conformance section. This additive approach helps to make it clear that sites which conform to WCAG 2.1 also conform to WCAG 2.0, thereby meeting conformance obligations that are specific to WCAG 2.0. The Accessibility Guidelines Working Group recommends that sites adopt WCAG 2.1 as their new conformance target, even if formal obligations mention WCAG 2.0, to provide improved accessibility and to anticipate future policy changes.
The following Success Criteria are new in WCAG 2.1:
1.3.4
Orientation
(AA)
1.3.5
Identify Input Purpose
(AA)
1.3.6
Identify Purpose
(AAA)
1.4.10
Reflow
(AA)
1.4.11
Non-Text Contrast
(AA)
1.4.12
Text Spacing
(AA)
1.4.13
Content on Hover or Focus
(AA)
2.1.4
Character Key Shortcuts
(A)
2.2.6
Timeouts
(AAA)
2.3.3
Animation from Interactions
(AAA)
2.5.1
Pointer Gestures
(A)
2.5.2
Pointer Cancellation
(A)
2.5.3
Label in Name
(A)
2.5.4
Motion Actuation
(A)
2.5.5
Target Size
(AAA)
2.5.6
Concurrent Input Mechanisms
(AAA)
4.1.3
Status Messages
(AA)
Many of these success criteria reference new terms that have also been added to the glossary and form part of the normative requirements of the success criteria.
In the Conformance section, a third note about page variants has been added to
Full Pages
, and an option for machine-readable metadata added to
Optional Components of a Conformance Claim
0.5.2
Numbering in WCAG 2.1
In order to avoid confusion for implementers for whom backwards compatibility to WCAG 2.0 is important, new success criteria in WCAG 2.1 have been appended to the end of the set of success criteria within their guideline. This avoids the need to change the section number of success criteria from WCAG 2.0, which would be caused by inserting new success critera between existing success ccriteria in the guideline, but it means success criteria in each guideline are no longer grouped by conformance level. The order of success criteria within each guideline does not imply information about conformance level; only the conformance level indicator (A / AA / AAA) on the success criterion itself indicates this. The
WCAG 2.1 Quick Reference
provides ways to view success criteria grouped by conformance level, along with many other filter and sort options.
0.5.3
Conformance to WCAG 2.1
WCAG 2.1 uses the same conformance model as WCAG 2.0 with a couple additions, which is described in the
Conformance
section. It is intended that sites that conform to WCAG 2.1 also conform to WCAG 2.0, which means they meet the requirements of any policies that reference WCAG 2.0, while also better meeting the needs of users on the current Web.
0.6
Later Versions of Accessibility Guidelines
In parallel with WCAG 2.1, the Accessibility Guidelines Working Group is developing another major version of accessibility guidelines. The result of this work is expected to be a more substantial restructuring of web accessibility guidance than would be realistic for dot-releases of WCAG 2. The work follows a research-focused, user-centered design methodology to produce the most effective and flexible outcome, including the roles of content authoring, user agent support, and authoring tool support. This is a multi-year effort, so WCAG 2.1 is needed as an interim measure to provide updated web accessibility guidance to reflect changes on the web since the publication of WCAG 2.0. The Working Group might also develop additional interim versions, continuing with WCAG 2.2, on a similar short timeline to provide additional support while the major version is completed.
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.
Success Criterion 1.1.1
Non-text Content
Understanding Non-text Content
How to Meet Non-text Content
(Level A)
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.
Controls, Input
If non-text content is a control or accepts user input, then it has a
name
that describes its purpose. (Refer to
Success Criterion 4.1.2
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 1.2
Time-based Media
Provide alternatives for time-based media.
Success Criterion 1.2.1
Audio-only and Video-only (Prerecorded)
Understanding Audio-only and Video-only (Prerecorded)
How to Meet Audio-only and Video-only (Prerecorded)
(Level A)
For
prerecorded
audio-only
and prerecorded
video-only
media, the following are true, except when the audio or video is a
media alternative for text
and is clearly labeled as such:
Prerecorded Audio-only
An
alternative for time-based media
is provided that presents equivalent information for prerecorded audio-only content.
Prerecorded Video-only
Either an alternative for time-based media or an audio track is provided that presents
equivalent information for prerecorded video-only content.
Success Criterion 1.2.2
Captions (Prerecorded)
Understanding Captions (Prerecorded)
How to Meet Captions (Prerecorded)
(Level A)
Captions
are provided for all
prerecorded
audio
content in
synchronized media
, except when the media is a
media alternative for text
and is clearly labeled as such.
Success Criterion 1.2.3
Audio Description or Media Alternative (Prerecorded)
Understanding Audio Description or Media Alternative (Prerecorded)
How to Meet Audio Description or Media Alternative (Prerecorded)
(Level A)
An
alternative for time-based media
or
audio description
of the
prerecorded
video
content is provided for
synchronized media
, except when the media is a
media alternative for text
and is clearly labeled as such.
Success Criterion 1.2.4
Captions (Live)
Understanding Captions (Live)
How to Meet Captions (Live)
(Level AA)
Captions
are provided for all
live
audio
content in
synchronized media
Success Criterion 1.2.5
Audio Description (Prerecorded)
Understanding Audio Description (Prerecorded)
How to Meet Audio Description (Prerecorded)
(Level AA)
Audio description
is provided for all
prerecorded
video
content in
synchronized media
Success Criterion 1.2.6
Sign Language (Prerecorded)
Understanding Sign Language (Prerecorded)
How to Meet Sign Language (Prerecorded)
(Level AAA)
Sign language interpretation
is provided for all
prerecorded
audio
content in
synchronized media
Success Criterion 1.2.7
Extended Audio Description (Prerecorded)
Understanding Extended Audio Description (Prerecorded)
How to Meet Extended Audio Description (Prerecorded)
(Level AAA)
Where pauses in foreground audio are insufficient to allow
audio descriptions
to convey the sense of the video,
extended audio description
is provided for all
prerecorded
video
content in
synchronized media
Success Criterion 1.2.8
Media Alternative (Prerecorded)
Understanding Media Alternative (Prerecorded)
How to Meet Media Alternative (Prerecorded)
(Level AAA)
An
alternative for time-based media
is provided for all
prerecorded
synchronized media
and for all prerecorded
video-only
media.
Success Criterion 1.2.9
Audio-only (Live)
Understanding Audio-only (Live)
How to Meet Audio-only (Live)
(Level AAA)
An
alternative for time-based media
that presents equivalent information for
live
audio-only
content is provided.
Guideline 1.3
Adaptable
Create content that can be presented in different ways (for example simpler layout) without losing information or structure.
Success Criterion 1.3.1
Info and Relationships
Understanding Info and Relationships
How to Meet Info and Relationships
(Level A)
Information,
structure
, and
relationships
conveyed through
presentation
can be
programmatically determined
or are available in text.
Success Criterion 1.3.2
Meaningful Sequence
Understanding Meaningful Sequence
How to Meet Meaningful Sequence
(Level A)
When the sequence in which content is presented affects its meaning, a
correct reading sequence
can be
programmatically determined
Success Criterion 1.3.3
Sensory Characteristics
Understanding Sensory Characteristics
How to Meet Sensory Characteristics
(Level A)
Instructions provided for understanding and operating content do not rely solely on
sensory characteristics of components such as shape, color, size, visual location, orientation,
or sound.
Note
For requirements related to color, refer to
Guideline 1.4
Success Criterion 1.3.4
Orientation
Understanding Orientation
How to Meet Orientation
(Level AA)
Content does not restrict its view and operation to a single display orientation, such as portrait or landscape, unless a specific display orientation is
essential
Note
Examples where a particular display orientation may be essential are a bank check, a piano application, slides for a projector or television, or virtual reality content where binary display orientation is not applicable.
Success Criterion 1.3.5
Identify Input Purpose
Understanding Identify Input Purpose
How to Meet Identify Input Purpose
(Level AA)
The purpose of each input field collecting information about the user can be
programmatically determined
when:
The input field serves a purpose identified in the
Input Purposes for User Interface Components section
; and
The content is implemented using technologies with support for identifying the expected meaning for form input data.
Success Criterion 1.3.6
Identify Purpose
Understanding Identify Purpose
How to Meet Identify Purpose
(Level AAA)
In content implemented using markup languages, the purpose of
User Interface Components
, icons, and
regions
can be
programmatically determined
Guideline 1.4
Distinguishable
Make it easier for users to see and hear content including separating foreground from background.
Success Criterion 1.4.1
Use of Color
Understanding Use of Color
How to Meet Use of Color
(Level A)
Color is not used as the only visual means of conveying information, indicating an
action, prompting a response, or distinguishing a visual element.
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.
Success Criterion 1.4.2
Audio Control
Understanding Audio Control
How to Meet Audio Control
(Level A)
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.
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
Success Criterion 1.4.3
Contrast (Minimum)
Understanding Contrast (Minimum)
How to Meet Contrast (Minimum)
(Level AA)
The visual presentation of
text
and
images of text
has a
contrast ratio
of at least 4.5:1, except for the following:
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 contrast requirement.
Success Criterion 1.4.4
Resize text
Understanding Resize text
How to Meet Resize text
(Level AA)
Except for
captions
and
images of text
text
can be resized without
assistive technology
up to 200 percent without loss of content or functionality.
Success Criterion 1.4.5
Images of Text
Understanding Images of Text
How to Meet Images of Text
(Level AA)
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:
Customizable
The image of text can be
visually customized
to the user's requirements;
Essential
A particular presentation of text is
essential
to the information being conveyed.
Note
Logotypes (text that is part of a logo or brand name) are considered essential.
Success Criterion 1.4.6
Contrast (Enhanced)
Understanding Contrast (Enhanced)
How to Meet Contrast (Enhanced)
(Level AAA)
The visual presentation of
text
and
images of text
has a
contrast ratio
of at least 7:1, except for the following:
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 contrast requirement.
Success Criterion 1.4.7
Low or No Background Audio
Understanding Low or No Background Audio
How to Meet Low or No Background Audio
(Level AAA)
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:
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.
Success Criterion 1.4.8
Visual Presentation
Understanding Visual Presentation
How to Meet Visual Presentation
(Level AAA)
For the visual presentation of
blocks of text
, a
mechanism
is available to achieve the following:
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
Success Criterion 1.4.9
Images of Text (No Exception)
Understanding Images of Text (No Exception)
How to Meet Images of Text (No Exception)
(Level AAA)
Images of text
are only used for
pure decoration
or where a particular presentation of
text
is
essential
to the information being conveyed.
Note
Logotypes (text that is part of a logo or brand name) are considered essential.
Success Criterion 1.4.10
Reflow
Understanding Reflow
How to Meet Reflow
(Level AA)
Content can be presented without loss of information or functionality, and without requiring scrolling in two dimensions for:
Vertical scrolling content at a width equivalent to 320
CSS pixels
Horizontal scrolling content at a height equivalent to 256
CSS pixels
Except for parts of the content which require two-dimensional layout for usage or meaning.
Note
Note: 320 CSS pixels is equivalent to a starting viewport width of 1280 CSS pixels wide at 400% zoom. For web content which are designed to scroll horizontally (e.g. with vertical text), the 256 CSS pixels is equivalent to a starting viewport height of 1024px at 400% zoom.
Note
Examples of content which require two-dimensional layout are images, maps, diagrams,
video, games, presentations, data tables, and interfaces where it is necessary to keep toolbars in view while
manipulating content.
Success Criterion 1.4.11
Non-text Contrast
Understanding Non-text Contrast
How to Meet Non-text Contrast
(Level AA)
The visual
presentation
of the following have a
contrast ratio
of at least 3:1 against adjacent color(s):
User Interface Components
Visual information required to identify
user interface components
and
states
, except for inactive components or where the appearance of the component is determined by the user agent and not modified by the author;
Graphical Objects
Parts of graphics required to understand the content, except when a particular presentation of graphics is
essential
to the information being conveyed.
Success Criterion 1.4.12
Text Spacing
Understanding Text Spacing
How to Meet Text Spacing
(Level AA)
In content implemented using markup languages that support the following
text
style properties
, no loss of content or functionality occurs by setting all of the following and by changing no other style property:
Line height (line spacing) to at least 1.5 times the font size;
Spacing following paragraphs to at least 2 times the font size;
Letter spacing (tracking) to at least 0.12 times the font size;
Word spacing to at least 0.16 times the font size.
Exception: Human languages and scripts that do not make use of one or more of these text style properties in written text can conform using only the properties that exist for that combination of language and script.
Success Criterion 1.4.13
Content on Hover or Focus
Understanding Content on Hover or Focus
How to Meet Content on Hover or Focus
(Level AA)
Where receiving and then removing pointer hover or keyboard focus triggers additional content to become visible and then hidden, the following are true:
Dismissable
mechanism
is available to dismiss the additional content without moving pointer hover or keyboard focus, unless the additional content communicates an
input error
or does not obscure or replace other content;
Hoverable
If pointer hover can trigger the additional content, then the pointer can be moved over the additional content without the additional content disappearing;
Persistent
The additional content remains visible until the hover or focus trigger is removed, the user dismisses it, or its information is no longer valid.
Exception: The visual presentation of the additional content is controlled by the user agent and is not modified by the author.
Note
Examples of additional content controlled by the user agent include browser tooltips created through use of the HTML
title
attribute
Note
Custom tooltips, sub-menus, and other nonmodal popups that display on hover and focus are examples of additional content covered by this criterion.
2.
Operable
User interface components and navigation must be operable.
Guideline 2.1
Keyboard Accessible
Make all functionality available from a keyboard.
Success Criterion 2.1.1
Keyboard
Understanding Keyboard
How to Meet Keyboard
(Level A)
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.
Note
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
This does not forbid and should not discourage providing mouse input or other input
methods in addition to keyboard operation.
Success Criterion 2.1.2
No Keyboard Trap
Understanding No Keyboard Trap
How to Meet No Keyboard Trap
(Level A)
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.
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
Success Criterion 2.1.3
Keyboard (No Exception)
Understanding Keyboard (No Exception)
How to Meet Keyboard (No Exception)
(Level AAA)
All
functionality
of the content is operable through a
keyboard interface
without requiring specific timings for individual keystrokes.
Success Criterion 2.1.4
Character Key Shortcuts
Understanding Character Key Shortcuts
How to Meet Character Key Shortcuts
(Level A)
If a
keyboard shortcut
is implemented in content using only letter (including upper- and lower-case letters), punctuation, number, or symbol characters, then at least one of the following is true:
Turn off
mechanism
is available to turn the shortcut off;
Remap
A mechanism is available to remap the shortcut to use one or more non-printable keyboard characters (e.g. Ctrl, Alt, etc);
Active only on focus
The keyboard shortcut for a
user interface component
is only active when that component has focus.
Guideline 2.2
Enough Time
Provide users enough time to read and use content.
Success Criterion 2.2.1
Timing Adjustable
Understanding Timing Adjustable
How to Meet Timing Adjustable
(Level A)
For each time limit that is set by the content, at least one of the following is true:
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.
Success Criterion 2.2.2
Pause, Stop, Hide
Understanding Pause, Stop, Hide
How to Meet Pause, Stop, Hide
(Level A)
For moving,
blinking
, scrolling, or auto-updating information, all of the following are true:
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
For requirements related to flickering or flashing content, refer to
Guideline 2.3
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
Note
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
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.
Success Criterion 2.2.3
No Timing
Understanding No Timing
How to Meet No Timing
(Level AAA)
Timing is not an
essential
part of the event or activity presented by the content, except for non-interactive
synchronized media
and
real-time events
Success Criterion 2.2.4
Interruptions
Understanding Interruptions
How to Meet Interruptions
(Level AAA)
Interruptions can be postponed or suppressed by the user, except interruptions involving
an
emergency
Success Criterion 2.2.5
Re-authenticating
Understanding Re-authenticating
How to Meet Re-authenticating
(Level AAA)
When an authenticated session expires, the user can continue the activity without
loss of data after re-authenticating.
Success Criterion 2.2.6
Timeouts
Understanding Timeouts
How to Meet Timeouts
(Level AAA)
Users are warned of the duration of any
user inactivity
that could cause data loss, unless the data is preserved for more than 20 hours when the user does not take any actions.
Note
Privacy regulations may require explicit user consent before user identification has been authenticated and before user data is preserved. In cases where the user is a minor, explicit consent may not be solicited in most jurisdictions, countries or regions. Consultation with privacy professionals and legal counsel is advised when considering data preservation as an approach to satisfy this success criterion.
Guideline 2.3
Seizures and Physical Reactions
Do not design content in a way that is known to cause seizures or physical reactions.
Success Criterion 2.3.1
Three Flashes or Below Threshold
Understanding Three Flashes or Below Threshold
How to Meet Three Flashes or Below Threshold
(Level A)
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
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
Success Criterion 2.3.2
Three Flashes
Understanding Three Flashes
How to Meet Three Flashes
(Level AAA)
Web pages
do not contain anything that
flashes
more than three times in any one second period.
Success Criterion 2.3.3
Animation from Interactions
Understanding Animation from Interactions
How to Meet Animation from Interactions
(Level AAA)
Motion animation
triggered by interaction can be disabled, unless the animation is
essential
to the functionality or the information being conveyed.
Guideline 2.4
Navigable
Provide ways to help users navigate, find content, and determine where they are.
Success Criterion 2.4.1
Bypass Blocks
Understanding Bypass Blocks
How to Meet Bypass Blocks
(Level A)
mechanism
is available to bypass blocks of content that are repeated on multiple
Web pages
Success Criterion 2.4.2
Page Titled
Understanding Page Titled
How to Meet Page Titled
(Level A)
Web pages
have titles that describe topic or purpose.
Success Criterion 2.4.3
Focus Order
Understanding Focus Order
How to Meet Focus Order
(Level A)
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.
Success Criterion 2.4.4
Link Purpose (In Context)
Understanding Link Purpose (In Context)
How to Meet Link Purpose (In Context)
(Level A)
The
purpose of each link
can be determined from the link text alone or from the link text together with its
programmatically determined link context
, except where the purpose of the link would be
ambiguous to users in general
Success Criterion 2.4.5
Multiple Ways
Understanding Multiple Ways
How to Meet Multiple Ways
(Level AA)
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
Success Criterion 2.4.6
Headings and Labels
Understanding Headings and Labels
How to Meet Headings and Labels
(Level AA)
Headings and
labels
describe topic or purpose.
Success Criterion 2.4.7
Focus Visible
Understanding Focus Visible
How to Meet Focus Visible
(Level AA)
Any keyboard operable user interface has a mode of operation where the keyboard focus
indicator is visible.
Success Criterion 2.4.8
Location
Understanding Location
How to Meet Location
(Level AAA)
Information about the user's location within a
set of Web pages
is available.
Success Criterion 2.4.9
Link Purpose (Link Only)
Understanding Link Purpose (Link Only)
How to Meet Link Purpose (Link Only)
(Level AAA)
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
Success Criterion 2.4.10
Section Headings
Understanding Section Headings
How to Meet Section Headings
(Level AAA)
Section
headings are used to organize the content.
Note
"Heading" is used in its general sense and includes titles and other ways to add a
heading to different types of content.
Note
This success criterion covers sections within writing, not
user interface components
. User Interface components are covered under
Success Criterion 4.1.2
Guideline 2.5
Input Modalities
Make it easier for users to operate functionality through various inputs beyond keyboard.
Success Criterion 2.5.1
Pointer Gestures
Understanding Pointer Gestures
How to Meet Pointer Gestures
(Level A)
All
functionality
that uses multipoint or path-based gestures for operation can be operated with a
single pointer
without a path-based gesture, unless a multipoint or path-based gesture is
essential
Note
This requirement applies to web content that interprets pointer actions (i.e. this does not apply to actions that are required to operate the user agent or assistive technology).
Success Criterion 2.5.2
Pointer Cancellation
Understanding Pointer Cancellation
How to Meet Pointer Cancellation
(Level A)
For
functionality
that can be operated using a
single pointer
, at least one of the following is true:
No Down-Event
The
down-event
of the pointer is not used to execute any part of the function;
Abort or Undo
Completion of the function is on the
up-event
, and a
mechanism
is available to abort the function before completion or to undo the function after completion;
Up Reversal
The up-event reverses any outcome of the preceding down-event;
Essential
Completing the function on the down-event is
essential
Note
Functions that emulate a keyboard or numeric keypad key press are considered essential.
Note
This requirement applies to web content that interprets pointer actions (i.e. this does not apply to actions that are required to operate the user agent or assistive technology).
Success Criterion 2.5.3
Label in Name
Understanding Label in Name
How to Meet Label in Name
(Level A)
For
user interface components
with
labels
that include
text
or
images of text
, the
name
contains the text that is presented visually.
Note
A best practice is to have the text of the label at the start of the name.
Success Criterion 2.5.4
Motion Actuation
Understanding Motion Actuation
How to Meet Motion Actuation
(Level A)
Functionality
that can be operated by device motion or user motion can also be operated by
user interface components
and responding to the motion can be disabled to prevent accidental actuation, except when:
Supported Interface
The motion is used to operate functionality through an
accessibility supported
interface;
Essential
The motion is
essential
for the function and doing so would invalidate the activity.
Success Criterion 2.5.5
Target Size
Understanding Target Size
How to Meet Target Size
(Level AAA)
The size of the
target
for
pointer inputs
is at least 44 by 44
CSS pixels
except when:
Equivalent
The target is available through an equivalent link or control on the same page that is at least 44 by 44 CSS pixels;
Inline
The target is in a sentence or block of text;
User Agent Control
The size of the target is determined by the user agent and is not modified by the author;
Essential
A particular presentation of the target is
essential
to the information being conveyed.
Success Criterion 2.5.6
Concurrent Input Mechanisms
Understanding Concurrent Input Mechanisms
How to Meet Concurrent Input Mechanisms
(Level AAA)
Web content does not restrict use of input modalities available on a platform except where the restriction is
essential
, required to ensure the security of the content, or required to respect user settings.
3.
Understandable
Information and the operation of user interface must be understandable.
Guideline 3.1
Readable
Make text content readable and understandable.
Success Criterion 3.1.1
Language of Page
Understanding Language of Page
How to Meet Language of Page
(Level A)
The default
human language
of each
Web page
can be
programmatically determined
Success Criterion 3.1.2
Language of Parts
Understanding Language of Parts
How to Meet Language of Parts
(Level AA)
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.
Success Criterion 3.1.3
Unusual Words
Understanding Unusual Words
How to Meet Unusual Words
(Level AAA)
mechanism
is available for identifying specific definitions of words or phrases
used in an unusual or restricted way
, including
idioms
and
jargon
Success Criterion 3.1.4
Abbreviations
Understanding Abbreviations
How to Meet Abbreviations
(Level AAA)
mechanism
for identifying the expanded form or meaning of
abbreviations
is available.
Success Criterion 3.1.5
Reading Level
Understanding Reading Level
How to Meet Reading Level
(Level AAA)
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.
Success Criterion 3.1.6
Pronunciation
Understanding Pronunciation
How to Meet Pronunciation
(Level AAA)
mechanism
is available for identifying specific pronunciation of words where meaning of the
words, in context, is ambiguous without knowing the pronunciation.
Guideline 3.2
Predictable
Make Web pages appear and operate in predictable ways.
Success Criterion 3.2.1
On Focus
Understanding On Focus
How to Meet On Focus
(Level A)
When any
user interface component
receives focus, it does not initiate a
change of context
Success Criterion 3.2.2
On Input
Understanding On Input
How to Meet On Input
(Level A)
Changing the setting of any
user interface component
does not automatically cause a
change of context
unless the user has been advised of the behavior before using the component.
Success Criterion 3.2.3
Consistent Navigation
Understanding Consistent Navigation
How to Meet Consistent Navigation
(Level AA)
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.
Success Criterion 3.2.4
Consistent Identification
Understanding Consistent Identification
How to Meet Consistent Identification
(Level AA)
Components that have the
same functionality
within a
set of Web pages
are identified consistently.
Success Criterion 3.2.5
Change on Request
Understanding Change on Request
How to Meet Change on Request
(Level AAA)
Changes of context
are initiated only by user request or a
mechanism
is available to turn off such changes.
Guideline 3.3
Input Assistance
Help users avoid and correct mistakes.
Success Criterion 3.3.1
Error Identification
Understanding Error Identification
How to Meet Error Identification
(Level A)
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.
Success Criterion 3.3.2
Labels or Instructions
Understanding Labels or Instructions
How to Meet Labels or Instructions
(Level A)
Labels
or instructions are provided when content requires user input.
Success Criterion 3.3.3
Error Suggestion
Understanding Error Suggestion
How to Meet Error Suggestion
(Level AA)
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.
Success Criterion 3.3.4
Error Prevention (Legal, Financial, Data)
Understanding Error Prevention (Legal, Financial, Data)
How to Meet Error Prevention (Legal, Financial, Data)
(Level AA)
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:
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.
Success Criterion 3.3.5
Help
Understanding Help
How to Meet Help
(Level AAA)
Context-sensitive help
is available.
Success Criterion 3.3.6
Error Prevention (All)
Understanding Error Prevention (All)
How to Meet Error Prevention (All)
(Level AAA)
For
Web pages
that require the user to submit information, at least one of the following is true:
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.
4.
Robust
Content must be robust enough that it can be interpreted by 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.
Success Criterion 4.1.1
Parsing
Understanding Parsing
How to Meet Parsing
(Level A)
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.
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.
Success Criterion 4.1.2
Name, Role, Value
Understanding Name, Role, Value
How to Meet Name, Role, Value
(Level A)
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
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.
Success Criterion 4.1.3
Status Messages
Understanding Status Messages
How to Meet Status Messages
(Level AA)
In content implemented using markup languages,
status messages
can be
programmatically determined
through
role
or properties such that they can be presented to the user by
assistive technologies
without receiving focus.
5.
Conformance
This section lists requirements for
conformance
to WCAG 2.1. 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.
5.1
Interpreting Normative Requirements
The main content of WCAG 2.1 is
normative
and defines requirements that impact conformance claims. Introductory material, appendices, sections marked as "non-normative", diagrams, examples, and notes are
informative
(non-normative). Non-normative material provides advisory information to help interpret the guidelines but does not create requirements that impact a conformance claim.
The key words
MAY
MUST
MUST NOT
NOT RECOMMENDED
RECOMMENDED
SHOULD
, and
SHOULD NOT
are to be interpreted as described in [
RFC2119
].
5.2
Conformance Requirements
In order for a Web page to conform to WCAG 2.1, all of the following conformance requirements must be satisfied:
5.2.1
Conformance Level
One of the following levels of conformance is met in full.
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.
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.
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
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
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.
5.2.2
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
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
Authors of Web pages that cannot conform due to content outside of the author's control may consider a
Statement of Partial Conformance
Note
New
A full page includes each variation of the page that is automatically presented by the page for various screen sizes (e.g. variations in a responsive Web page). Each of these variations needs to conform (or needs to have a conforming alternate version) in order for the entire page to conform.
5.2.3
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.)
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.
5.2.4
Only Accessibility-Supported Ways of Using Technologies
Only
accessibility-supported
ways of using
technologies
are
relied upon
to satisfy the success criteria. Any information or functionality that is provided in a way that is not accessibility supported is also available in a way that is accessibility supported. (See
Understanding accessibility support
.)
5.2.5
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
5.3
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.
5.3.1
Required Components of a Conformance Claim
Conformance claims are
not required
. Authors can conform to WCAG 2.1 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 2.1 at
In WCAG 2.0 this was a dated URI, which may need to be adjusted when this becomes a Rec.
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
The Web pages may be described by list or by an expression that describes all of the URIs included in the claim.
Note
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.
5.3.2
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.
A list of specific accessibility characteristics of the content, provided in machine-readable metadata.
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.
Note
Refer to
Understanding Conformance Claims
for more information and example conformance claims.
Note
Refer to
Understanding Metadata
for more information about the use of metadata in conformance claims.
5.4
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 2.1 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.)
5.5
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 2.1 at level X if accessibility support existed for the following language(s):"
6.
Glossary
abbreviation
shortened form of a word, phrase, or name where the abbreviation has not become part
of the language
Note
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
Not defined in all languages.
SNCF is a French initialism that contains the initial letters of the
Société Nationale des Chemins de Fer
, the French national railroad.
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
NOAA is an acronym made from the initial letters of the National Oceanic and Atmospheric
Administration in the United States.
Note
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:
does not cost a person with a disability any more than a person without a disability
and
is as easy to find and obtain for a person with a disability as it is for a person
without disabilities.
Note
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
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 Criterion 4
and
Conformance Criterion 5
, are met.
Note
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
When citing Web content technologies that have multiple versions, the version(s) supported
should be specified.
Note
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)
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
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
Assistive technologies often communicate data and messages with mainstream user agents
by using and monitoring APIs.
Note
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.
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
Audio description of
video
provides information about actions, characters, scene changes, on-screen text, and
other visual content.
Note
In standard audio description, narration is added during existing pauses in dialogue.
(See also
extended audio description
.)
Note
Where all of the
video
information is already provided in existing
audio
, no additional audio description is necessary.
Note
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
CAPTCHA tests often involve asking the user to type in text that is displayed in an
obscured image or audio file.
Note
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.
captions
synchronized visual and/or
text alternative
for both speech and non-speech audio information needed to understand the media content
Note
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
Closed Captions are equivalents that can be turned on and off with some players.
Note
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
Captions should not obscure or obstruct relevant information in the video.
Note
In some countries, captions are called subtitles.
Note
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).
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
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
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
If multiple language versions are available, then conforming alternate versions are
required for each language offered.
Note
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
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
Alternate versions should not be confused with
supplementary content
, which support the original page and enhance comprehension.
Note
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
L1 is the
relative luminance
of the lighter of the colors, and
L2 is the
relative luminance
of the darker of the colors.
Note
Contrast ratios can range from 1 to 21 (commonly written 1:1 to 21:1).
Note
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
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
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
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
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
CSS pixel
visual angle of about 0.0213 degrees
A CSS pixel is the canonical unit of measure for all lengths and measurements in CSS.
This unit is density-independent, and distinct from actual hardware pixels present
in a display. User agents and operating systems should ensure that a CSS pixel is
set as closely as possible to the
CSS Values and Units Module Level 3 reference pixel
css3-values
], which takes into account the physical dimensions of the display
and the assumed viewing distance (factors that cannot be determined by content authors).
down-event
platform event that occurs when the trigger stimulus of a pointer is depressed
The down-event may have different names on different platforms, such as "touchstart" or "mousedown".
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
Note
See
general flash and red flash thresholds
for information about types of flash that are not allowed.
Note
See also
blinking
functionality
processes
and outcomes achievable through user action
general flash and red flash thresholds
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:
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
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
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
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
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
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
Note
See also
sign language
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.
In English, "spilling the beans" means "revealing a secret." However, "knocking over
the beans" or "spilling the vegetables" does not mean the same thing.
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.
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.
A person's name on a nametag in a photograph.
informative
for information purposes and not required for conformance
Note
Content required for
conformance
is referred to as "
normative
."
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
The word StickyKeys is jargon from the field of assistive technology/accessibility.
keyboard interface
interface used by software to obtain keystroke input
Note
A keyboard interface allows users to provide keystroke input to programs even if the
native technology does not contain a keyboard.
Note
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
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.
keyboard shortcut
alternative means of triggering an action by the pressing of one or more keys
label
text
or other component with a
text alternative
that is presented to a user to identify a component within Web
content
Note
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
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
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
Font size is the size when the content is delivered. It does not include resizing
that may be done by a user.
Note
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
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
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
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
A broadcast delay is a short (usually automated) delay, for example used in order
to give the broadcaster time to cue or censor the audio (or video) feed, but not sufficient
to allow significant editing.
Note
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
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
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.
motion animation
addition of steps between conditions to create the illusion of movement or to give a sense of a smooth transition
For example, an element which moves into place or changes size while appearing is considered to be animated. An element which appears instantly without transitioning is not using animation. Motion animation does not include changes of color, blurring or opacity.
name
text by which software can identify a component within Web content to the user
Note
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
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
One may conform in a variety of well-defined ways to this document.
Note
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
pointer input
input device that can target a specific coordinate (or set of coordinates) on a screen,
such as a mouse, pen, or touch contact
See also
Pointer Events pointer definition
pointerevents
].
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
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.
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
Note
Determined in a markup language from elements and attributes that are accessed directly
by commonly available assistive technology.
Note
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
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.
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
A Webcast of a live performance (occurs at the same time as the viewing and is not
prerecorded).
An on-line auction with people bidding (occurs at the same time as the viewing).
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).
region
perceivable, programmatically determined section of content
Note
In HTML, any area designated with a landmark role would be a region.
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
For the sRGB colorspace, the relative luminance of a color is defined as L = 0.2126
+ 0.7152 *
+ 0.0722 *
where
and
are defined as:
if RsRGB <= 0.03928 then
= RsRGB/12.92 else
= ((RsRGB+0.055)/1.055) ^ 2.4
if GsRGB <= 0.03928 then
= GsRGB/12.92 else
= ((GsRGB+0.055)/1.055) ^ 2.4
if BsRGB <= 0.03928 then
= BsRGB/12.92 else
= ((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
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
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
Tools are available that automatically do the calculations when testing contrast and
flash.
Note
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
A number that indicates whether an image functions as a hyperlink, command button,
or check box.
same functionality
same result when used
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
Examples include a publication which is split across multiple Web pages, where each page contains
one chapter or other significant section of the work. The publication is logically
a single contiguous unit, and contains navigation features that enable access to the
full set of pages.
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.
single pointer
pointer input that operates with one point of contact with the screen, including single taps and clicks, double-taps and clicks, long presses, and path-based gestures
specific sensory experience
a sensory experience that is not purely decorative and does not primarily convey important
information or perform a function
Examples include a performance of a flute solo, works of visual art etc.
state
dynamic property expressing characteristics of a user interface component that may change in response to user action or automated processes
States do not affect the nature of the component, but represent data associated with the component or user interaction possibilities. Examples include focus, hover, select, press, check, visited/unvisited, and expand/collapse.
status message
change in content that is not a
change of context
, and that provides information to the user on the success or results of an action, on the waiting state of an application, on the progress of a process, or on the existence of errors
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
style property
property whose value determines the presentation (e.g. font, color, size, location, padding, volume, synthesized speech prosody) of
content elements as they are rendered (e.g. onscreen, via loudspeaker, via braille display) by user agents
Style properties can have several origins:
User agent default styles: The default style property values applied in the absence of any author or user styles. Some web content technologies specify a default rendering, others do not;
Author styles: Style property values that are set by the author as part of the content (e.g. in-line styles, author style
sheets);
User styles: Style property values that are set by the user (e.g. via user agent interface settings, user style sheets)
supplemental content
additional
content
that illustrates or clarifies the primary content
An audio version of a
Web page
An illustration of a complex
process
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
target
region of the display that will accept a pointer action, such as the interactive area of a user interface component
Note
If two or more touch targets are overlapping, the overlapping area should not be included in the measurement of the target size, except when the overlapping targets perform the same action or open the same page.
technology
(Web content)
mechanism
for encoding instructions to be rendered, played or executed by
user agents
Note
As used in these guidelines "Web Technology" and the word "technology" (when used
alone) both refer to Web Content Technologies.
Note
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.
Note
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.
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.
Note
Refer to
Understanding Text Alternatives
for more information.
up-event
platform event that occurs when the trigger stimulus of a pointer is released
The up-event may have different names on different platforms, such as "touchend" or "mouseup".
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
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 2.1, so a definition is supplied in the glossary.
user agent
any software that retrieves and presents Web content for users
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.
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
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
User interface components include form elements and links as well as components generated
by scripts.
Note
What is meant by "component" or "user interface component" here is also sometimes
called "user interface element".
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."
user inactivity
any continuous period of time where no user actions occur
The method of tracking will be determined by the web site or application.
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
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
This definition is based on
User Agent Accessibility Guidelines 1.0 Glossary
UAAG10
].
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
Although any "other resources" would be rendered together with the primary resource,
they would not necessarily be rendered simultaneously with each other.
Note
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.
A Web resource including all embedded images and media.
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.
A customizable portal site, where users can choose content to display from a set of
different content modules.
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.
7.
Input Purposes for User Interface Components
This section contains a listing of common
user interface component
input purposes. The terms below are not keywords that must be used, but instead represent purposes that must be captured in the taxonomy adopted by a webpage. Where applicable, authors mark up controls with the chosen taxonomy to indicate the semantic purpose. This provides the potential for user agents and assistive technologies to apply personalized presentations that can enable more people to understand and use the content.
Note
The list of input type purposes is based on the control purposes defined in the
HTML 5.2 Autofill field section
, but it is important to understand that a different technology may have some or all of the same concepts defined in its specification and only the concepts that are mapped to the meanings below are required.
The following input control purposes are intended to relate to the user of the content and pertain only to information related to that individual.
name
- Full name
honorific-prefix
- Prefix or title (e.g., "Mr.", "Ms.", "Dr.", "M
lle
")
given-name
- Given name (in some Western cultures, also known as the
first name
additional-name
- Additional names (in some Western cultures, also known as
middle names
, forenames other than the first name)
family-name
- Family name (in some Western cultures, also known as the
last name
or
surname
honorific-suffix
- Suffix (e.g., "Jr.", "B.Sc.", "MBASW", "II")
nickname
- Nickname, screen name, handle: a typically short name used instead of the full name
organization-title
- Job title (e.g., "Software Engineer", "Senior Vice President", "Deputy Managing Director")
username
- A username
new-password
- A new password (e.g., when creating an account or changing a password)
current-password
- The current password for the account identified by the
username
field (e.g., when logging in)
organization
- Company name corresponding to the person, address, or contact information in the other fields associated with this field
street-address
- Street address (multiple lines, newlines preserved)
address-line1
- Street address (one line per field, line 1)
address-line2
- Street address (one line per field, line 2)
address-line3
- Street address (one line per field, line 3)
address-level4
- The most fine-grained administrative level, in addresses with four administrative levels
address-level3
- The third administrative level, in addresses with three or more administrative levels
address-level2
- The second administrative level, in addresses with two or more administrative levels; in the countries with two administrative levels, this would typically be the city, town, village, or other locality within which the relevant street address is found
address-level1
- The broadest administrative level in the address, i.e., the province within which the locality is found; for example, in the US, this would be the state; in Switzerland it would be the canton; in the UK, the post town
country
- Country code
country-name
- Country name
postal-code
- Postal code, post code, ZIP code, CEDEX code (if CEDEX, append "CEDEX", and the
dissement
, if relevant, to the
address-level2
field)
cc-name
- Full name as given on the payment instrument
cc-given-name
- Given name as given on the payment instrument (in some Western cultures, also known as the
first name
cc-additional-name
- Additional names given on the payment instrument (in some Western cultures, also known as
middle names
, forenames other than the first name)
cc-family-name
- Family name given on the payment instrument (in some Western cultures, also known as the
last name
or
surname
cc-number
- Code identifying the payment instrument (e.g., the credit card number)
cc-exp
- Expiration date of the payment instrument
cc-exp-month
- Month component of the expiration date of the payment instrument
cc-exp-year
- Year component of the expiration date of the payment instrument
cc-csc
- Security code for the payment instrument (also known as the card security code (CSC), card validation code (CVC), card verification value (CVV), signature panel code (SPC), credit card ID (CCID), etc)
cc-type
- Type of payment instrument
transaction-currency
- The currency that the user would prefer the transaction to use
transaction-amount
- The amount that the user would like for the transaction (e.g., when entering a bid or sale price)
language
- Preferred language
bday
- Birthday
bday-day
- Day component of birthday
bday-month
- Month component of birthday
bday-year
- Year component of birthday
sex
- Gender identity (e.g., Female, Fa’afafine)
url
- Home page or other Web page corresponding to the company, person, address, or contact information in the other fields associated with this field
photo
- Photograph, icon, or other image corresponding to the company, person, address, or contact information in the other fields associated with this field
tel
- Full telephone number, including country code
tel-country-code
- Country code component of the telephone number
tel-national
- Telephone number without the county code component, with a country-internal prefix applied if applicable
tel-area-code
- Area code component of the telephone number, with a country-internal prefix applied if applicable
tel-local
- Telephone number without the country code and area code components
tel-local-prefix
- First part of the component of the telephone number that follows the area code, when that component is split into two components
tel-local-suffix
- Second part of the component of the telephone number that follows the area code, when that component is split into two components
tel-extension
- Telephone number internal extension code
email
- E-mail address
impp
- URL representing an instant messaging protocol endpoint (for example, "
aim:goim?screenname=example
" or "
xmpp:fred@example.net
")
A.
Acknowledgments
Additional information about participation in the Accessibility Guidelines Working Group (AG WG) can be found on the
Working Group home page
A.1
Participants of the AG WG active in the development of this document:
Jake Abma (Invited Expert)
Shadi Abou-Zahra (
W3C
Chuck Adams (Oracle Corporation)
Amani Ali (Nomensa)
Jim Allan (Invited Expert)
Paul Adam (Deque Systems, Inc.)
Christopher Auclair (VitalSource | Ingram Content Group)
Jon Avila (Level Access)
Tom Babinszki (IBM Corporation)
Bruce Bailey (U.S. Access Board)
Renaldo Bernard (University of Southampton)
Chris Blouch (Level Access)
Denis Boudreau (Deque Systems, Inc.)
Judy Brewer (
W3C
Shari Butler (Pearson plc)
Thaddeus Cambron (Invited Expert)
Alastair Campbell (Nomensa)
Laura Carlson (Invited Expert)
Louis Cheng (Google)
Pietro Cirrincione (Invited Expert)
Vivienne Conway (Web Key IT Pty Ltd)
Michael Cooper (
W3C
Romain Deltour (DAISY Consortium)
Wayne Dick (Knowbility, Inc)
Chaohai Ding (University of Southampton)
Kim Dirks (Thompson Reuters)
Shwetank Dixit (BarrierBreak Technologies)
Anthony Doran (TextHelp)
E.A. Draffan (University of Southampton)
Eric Eggert (
W3C
Michael Elledge (Invited Expert)
Wilco Fiers (Deque Systems, Inc.)
Detlev Fischer (Invited Expert)
John Foliot (Deque Systems, Inc.)
Matt Garrish (DAISY Consortium)
Alistair Garrison (Level Access)
Michael Gower (IBM Corporation)
Jon Gunderson
Markku Hakkinen (Educational Testing Service)
Katie Haritos-Shea (Knowbility, Inc)
Andy Heath (Invited Expert)
Shawn Henry (
W3C
Thomas Hoffman (Educational Testing Service)
Sarah Horton (The Paciello Group, LLC)
Stefan Johansson (Invited Expert)
Marc Johlic (IBM Corporation)
Rick Johnson (VitalSource | Ingram Content Group)
Crystal Jones (Microsoft Corporation)
Andrew Kirkpatrick (Adobe)
John Kirkwood (Invited Expert)
Jason Kiss (Department of Internal Affairs, New Zealand Government)
Maureen Kraft (IBM Corporation)
JaEun Ku (University of Illinois at Urbana-Champaign)
Patrick Lauke (The Paciello Group, LLC)
Shawn Lauriat (Google, Inc.)
Steve Lee (Invited Expert)
Alex Li (Microsoft Corporation)
Chris Loiselle (Invited Expert)
Greg Lowney (Invited Expert)
Adam Lund (Thomson Reuters)
David MacDonald (Invited Expert)
Erich Manser (IBM Corporation)
Kurt Mattes (Deque Systems, Inc.)
Scott McCormack (Level Access)
Chris McMeeking (Deque Systems, Inc.)
Jan McSorley (Pearson plc)
Neil Milliken (Unify Software and Solutions)
Rachael Montgomery (MITRE Corporation)
Mary Jo Mueller (IBM Corporation)
Brooks Newton (Thomson Reuters)
James Nurthen (Oracle Corporation)
Joshue O Connor (Invited Expert)
Sailesh Panchang (Deque Systems, Inc.)
Charu Pandhi (IBM Corporation)
Kim Patch (Invited Expert)
Melanie Philipp (Deque Systems, Inc.)
Mike Pluke (Invited Expert)
Ian Pouncey (The Paciello Group, LLC)
Ruoxi Ran (
W3C
Stephen Repsher (The Boeing Company)
Jan Richards (Invited Expert)
John Rochford (Invited Expert)
Marla Runyan (Invited Expert)
Stefan Schnabel (SAP SE)
Ayelet Seeman (Invited Expert)
Lisa Seeman-Kestenbaum (Invited Expert)
Glenda Sims (Deque Systems, Inc.)
Avneesh Singh (DAISY Consortium)
David Sloan (The Paciello Group, LLC)
Alan Smith (Invited Expert)
Jim Smith (Unify Software and Solutions)
Adam Solomon (Invited Expert)
Jaeil Song (National Information Society Agency (NIA))
Jeanne Spellman (The Paciello Group, LLC)
Makoto Ueki (Invited Expert)
Jatin Vaishnav (Deque Systems, Inc.)
Gregg Vanderheiden (Raising the Floor)
Evangelos Vlachogiannis (Fraunhofer Gesellschaft)
Kathleen Wahlbin (Invited Expert)
Can Wang (Zhejiang University)
Léonie Watson (The Paciello Group, LLC)
Jason White (Educational Testing Service)
Mark Wilcock (Unify Software and Solutions)
A.2
Other previously active WCAG WG participants and other contributors to WCAG 2.0, WCAG 2.1, or supporting resources
Paul Adam, Jenae Andershonis, Wilhelm Joys Andersen, Andrew Arch, Avi Arditti, Aries Arditi, Mark Barratt, Mike Barta, Sandy Bartell, Kynn Bartlett, Chris Beer, Charles Belov, Marco Bertoni, Harvey Bingham, Chris Blouch, Paul Bohman, Frederick Boland, Denis Boudreau, Patrice Bourlon, Andy Brown, Dick Brown, Doyle Burnett, Raven Calais, Ben Caldwell, Tomas Caspers, Roberto Castaldo, Sofia Celic-Li, Sambhavi Chandrashekar, Mike Cherim, Jonathan Chetwynd, Wendy Chisholm, Alan Chuter, David M Clark, Joe Clark, Darcy Clarke, James Coltham, Earl Cousins, James Craig, Tom Croucher, Pierce Crowell, Nir Dagan, Daniel Dardailler, Geoff Deering, Sébastien Delorme, Pete DeVasto, Iyad Abu Doush, Sylvie Duchateau, Cherie Eckholm, Roberto Ellero, Don Evans, Gavin Evans, Neal Ewers, Steve Faulkner, Bengt Farre, Lainey Feingold, Wilco Fiers, Michel Fitos, Alan J. Flavell, Nikolaos Floratos, Kentarou Fukuda, Miguel Garcia, P.J. Gardner, Alistair Garrison, Greg Gay, Becky Gibson, Al Gilman, Kerstin Goldsmith, Michael Grade, Karl Groves, Loretta Guarino Reid, Jon Gunderson, Emmanuelle Gutiérrez y Restrepo, Brian Hardy, Eric Hansen, Benjamin Hawkes-Lewis, Sean Hayes, Shawn Henry, Hans Hillen, Donovan Hipke, Bjoern Hoehrmann, Allen Hoffman, Chris Hofstader, Yvette Hoitink, Martijn Houtepen, Carlos Iglesias, Richard Ishida, Jonas Jacek, Ian Jacobs, Phill Jenkins, Barry Johnson, Duff Johnson, Jyotsna Kaki, Shilpi Kapoor, Leonard R. Kasday, Kazuhito Kidachi, Ken Kipness, Johannes Koch, Marja-Riitta Koivunen, Preety Kumar, Kristjan Kure, Andrew LaHart, Gez Lemon, Chuck Letourneau, Aurélien Levy, Harry Loots, Scott Luebking, Tim Lacy, Jim Ley, Alex Li, William Loughborough, N Maffeo, Mark Magennis, Kapsi Maria, Luca Mascaro, Matt May, Sheena McCullagh, Liam McGee, Jens Oliver Meiert, Niqui Merret, Jonathan Metz, Alessandro Miele, Steven Miller, Mathew J Mirabella, Matt May, Marti McCuller, Sorcha Moore, Charles F. Munat, Robert Neff, Charles Nevile, Liddy Nevile, Dylan Nicholson, Bruno von Niman, Tim Noonan, Sebastiano Nutarelli, Graham Oliver, Sean B. Palmer, Devarshi Pant, Nigel Peck, Anne Pemberton, David Poehlman, Ian Pouncey, Charles Pritchard, Kerstin Probiesch, W Reagan, Adam Victor Reed, Chris Reeve, Chris Ridpath, Lee Roberts, Mark Rogers, Raph de Rooij, Gregory J. Rosmaita, Matthew Ross, Sharron Rush, Joel Sanda, Janina Sajka, Roberto Scano, Gordon Schantz, Tim van Schie, Wolf Schmidt, Stefan Schnabel, Cynthia Shelly, Glenda Sims, John Slatin, Becky Smith, Jared Smith, Andi Snow-Weaver, Neil Soiffer, Mike Squillace, Michael Stenitzer, Diane Stottlemyer, Christophe Strobbe, Sarah J Swierenga, Jim Thatcher, Terry Thompson, Justin Thorp, David Todd, Mary Utt, Jean Vanderdonckt, Carlos A Velasco, Eric Velleman, Gijs Veyfeyken, Dena Wainwright, Paul Walsch, Daman Wandke, Richard Warren, Elle Waters, Takayuki Watanabe, Gian Wild, David Wooley, Wu Wei, Kenny Zhang, Leona Zumbo.
A.3
Enabling funders
This publication has been funded in part with U.S. Federal funds from the Health and Human Services, National Institute on Disability, Independent Living, and Rehabilitation Research (NIDILRR), initially under contract number ED-OSE-10-C-0067 and now under contract number HHSP23301500054C. The content of this publication does not necessarily reflect the views or policies of the U.S. Department of Health and Human Services or the U.S. Department of Education, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.
B.
References
B.1
Normative references
[css3-values]
CSS Values and Units Module Level 3
. Tab Atkins Jr.; Elika Etemad. W3C. 29 September 2016. W3C Candidate Recommendation. URL:
[pointerevents]
Pointer Events
. Jacob Rossi; Matt Brubeck. W3C. 24 February 2015. W3C Recommendation. URL:
[WCAG20]
Web Content Accessibility Guidelines (WCAG) 2.0
. Ben Caldwell; Michael Cooper; Loretta Guarino Reid; Gregg Vanderheiden et al. W3C. 11 December 2008. W3C Recommendation. URL:
B.2
Informative references
[HARDING-BINNIE]
Independent Analysis of the ITC Photosensitive Epilepsy Calibration Test Tape
. Harding G. F. A.; Binnie, C.D..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.
[RFC2119]
Key words for use in RFCs to Indicate Requirement Levels
. S. Bradner. IETF. March 1997. Best Current Practice. URL:
[sRGB]
A Standard Default Color Space for the Internet - sRGB, Version 1.10
. M. Stokes; M. Anderson; S. Chandrasekar; R. Motta.November 5, 1996. URL:
[UAAG10]
User Agent Accessibility Guidelines 1.0
. Ian Jacobs; Jon Gunderson; Eric Hansen. W3C. 17 December 2002. W3C Recommendation. URL:
[UNESCO]
International Standard Classification of Education
. 1997. URL:
[WAI-WEBCONTENT]
Web Content Accessibility Guidelines 1.0
. Wendy Chisholm; Gregg Vanderheiden; Ian Jacobs. W3C. 5 May 1999. W3C Recommendation. URL: