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 accessible to a wider range of people with disabilities, including blindness and low vision, deafness and hearing loss, learning disabilities, cognitive limitations, limited movement, speech disabilities, photosensitivity, and combinations of these. These guidelines address accessibility of web content on desktops, laptops, tablets, and mobile devices. Following these guidelines will also often make your 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, and therefore to policies that reference WCAG 2.0.

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.

This is a Working Draft of Web Content Accessibility Guidelines (WCAG) 2.1 by the Accessibility Guidelines Working Group. This draft includes only the success criteria that have been formally accepted by the Working Group, and not the proposed success criteria that were in the previous draft. Those proposals will be processed by the Working Group, refined, and if approved, included in future drafts. For more information on the status of WCAG 2.1 development, see WCAG 2.1 Status.

For this publication, the Accessibility Guidelines Working Group particularly seeks feedback on the following questions:

To comment, file an issue in the W3C WCAG 2.1 GitHub repository. Although the proposed Success Criteria in this document reference issues tracking discussion, 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 are requested by 9 May 2017. In-progress updates to the document may be viewed in the publicly visible editors' draft.

This document was published by the Accessibility Guidelines Working Group as a Working Draft. This document is intended to become a W3C Recommendation.

Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

This document is governed by the 1 March 2017 W3C Process Document.


This section is non-normative.

0.1 About This Draft§

This is a draft of the guidelines, published to allow initial review of the structure, approach, and types of new success criteria. It does not yet include all the Success Criteria that have been proposed for WCAG 2.1, nor are the ones present necessarily in their final form.

Because WCAG 2.1 extends WCAG 2.0, all the Success Criteria from WCAG 2.0 are included. To differentiate new Success Criteria, they are labeled as "[New]" and displayed in a green box. In this draft the WCAG 2.0 Success Criteria remain unchanged. This does create some redundancy but the Working Group seeks review of the new Success Criteria at this time and will evaluate where to modify existing WCAG 2.0 Success Criteria later in the process.

Not all Success Criteria proposals are included in the above list. The Working Group maintains a full set of current Success Criterion proposals which is also available for review and consideration for inclusion in future drafts.

0.2 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.

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:

Further introductory information about the structure of WCAG 2.0, inherited by WCAG 2.1, is available in the introduction to WCAG 2.0. For brevity in this draft it is not repeated here but can be found at:

0.3 Conformance to WCAG 2.1§

WCAG 2.1 uses the same conformance model as WCAG 2.0, which is described in the Conformance section. The conformance section has not been updated in this Working Draft to describe how WCAG 2.1 conformance builds upon WCAG 2.0 conformance. In particular, 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. Conformance wording for this will be provided in a future Working Draft.

0.4 Future work on WCAG 2.1§

The Accessibility Guidelines Working Group plans to continue developing WCAG 2.1 over the course of 2017. This work will primarily involve review and processing of the Success Criteria proposals, response to public feedback on this and later Working Drafts, and preparation of support materials similar to Understanding WCAG 2.0 [UNDERSTANDING-WCAG20] and Techniques for WCAG 2.0 [WCAG20-TECHS]. Early feedback on this work as soon as it is available is important, because the Working Group intends to begin finalization stages towards the end of the year.

Once the set of Success Criteria has been decided for WCAG 2.1, the Working Group will review the structure of the document. One goal will be to achieve the most clear backwards compatibility possible with WCAG 2.0; another will be to optimize the new Success Criteria to reduce duplication and increase clarity. The Working Group will also make final decisions about characteristics of the specification such as numbering and position of added Success Criteria. In preparation for the Candidate Recommendation, the Working Group will also re-evaluate testability and implementability of the Success Criteria given the technologies available at that time.

0.5 Later versions of Accessibility Guidelines§

In parallel with WCAG 2.1, the Accessibility Guidelines Working Group is working on requirements for a 3.0 version of accessibility guidelines, developed by the Silver Task Force. 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 task force 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.

In order for WCAG 2.1 to achieve its goal to update web accessibility guidance in a time frame that is meaningful before the 3.0 project delivers results, WCAG 2.1 must be completed quickly. This inherently means that some proposed Success Criteria may prove too complex to include in WCAG 2.1, but nonetheless will be viewed as important accessibility guidance for current web content. The larger 3.0 project is expected to incorporate such guidance, but the Working Group could also decide that another set of guidelines between WCAG 2.1 and 3.0 is needed. In that case, a new version, WCAG 2.2, could be proposed. A decision to develop WCAG 2.2 will need to balance the benefits of providing additional accessibility guidance earlier, versus the opportunity cost the work could have on the more substantially restructured and comprehensive 3.0 project. The current Accessibility Guidelines Working Group charter states "The Working Group intends to produce updated guidance for accessibility on a regular interval, starting with WCAG 2.1. Depending on the outcome of the requirements development for the next major update to WCAG, it may be necessary to pursue further dot-releases of WCAG until a major release is ready to be completed in time for a scheduled release date."

Principle 1. Perceivable §

Information and user interface components must be presentable to users in ways they can perceive.

Guideline 1.1 Text Alternatives§

Provide text alternatives for any non-text content so that it can be changed into other forms people need, such as large print, braille, speech, symbols or simpler language.

Success Criterion 1.1.1 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.)


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.


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.


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)§

(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)§

(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)§

(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)§

(Level AA)

Captions are provided for all live audio content in synchronized media.

Success Criterion 1.2.5 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)§

(Level AAA)

Sign language interpretation is provided for all prerecorded audio content in synchronized media.

Success Criterion 1.2.7 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)§

(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)§

(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§

(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§

(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§

(Level A)

Instructions provided for understanding and operating content do not rely solely on sensory characteristics of components such as shape, size, visual location, orientation, or sound.


For requirements related to color, refer to Guideline 1.4.

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§

(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.


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§

(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.


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)§

(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;


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.


Text that is part of a logo or brand name has no contrast requirement.

Success Criterion 1.4.4 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§

(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:


The image of text can be visually customized to the user's requirements;


A particular presentation of text is essential to the information being conveyed.


Logotypes (text that is part of a logo or brand name) are considered essential.

Success Criterion 1.4.6 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;


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.


Text that is part of a logo or brand name has no contrast requirement.

Success Criterion 1.4.7 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.


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§

(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)§

(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.


Logotypes (text that is part of a logo or brand name) are considered essential.

Success Criterion 1.4.10 Resize content§

(Level A)


Issue 1

Discussion of the issue is available in Issue 77 and Pull Request 120. To file comments on this proposal, please raise new issues for each discrete comment in GitHub.

Content can be resized to 400% without loss of content or functionality, and without requiring two-dimensional scrolling except for parts of the content where fixed spatial layout is necessary to use or meaning.

Success Criterion 1.4.11 Graphics Contrast§

(Level AA)


Editor's Note

Discussion of the issue is available in Issue 9 and Pull Request 100.

The visual presentation of graphical objects that are essential for understanding the content or functionality have a contrast ratio of at least 4.5:1 against the adjacent color(s), except for the following:

For graphical objects with a minimum width and height of at least 3 CSS pixels, the graphic has a contrast ratio of at least 3:1.
Non-text content that is primarily intended to create a visual sensory experience has no contrast requirement;
Graphics that are part of a logo or brand name have no minimum contrast requirement.
A particular presentation of the graphical is essential to the information being conveyed.

Principle 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§

(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.


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.


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§

(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.


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)§

(Level AAA)

All functionality of the content is operable through a keyboard interface without requiring specific timings for individual keystrokes.

Guideline 2.2 Enough Time§

Provide users enough time to read and use content.

Success Criterion 2.2.1 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


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


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.


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§

(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


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.


For requirements related to flickering or flashing content, refer to Guideline 2.3.


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.


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.


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§

(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§

(Level AAA)

Interruptions can be postponed or suppressed by the user, except interruptions involving an emergency.

Success Criterion 2.2.5 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 Interruptions (minimum)§

(Level AA)


Editor's Note

Discussion of the issue is available in Issue 47 and Pull Request 98.

There is an easily available mechanism to postpone and suppress interruptions and changes in content unless they are initiated by the user or involve an emergency.

Guideline 2.3 Seizures§

Do not design content in a way that is known to cause seizures.

Success Criterion 2.3.1 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.


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§

(Level AAA)

Web pages do not contain anything that flashes more than three times in any one second period.

Principle 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§

(Level A)

The default human language of each Web page can be programmatically determined.

Success Criterion 3.1.2 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§

(Level AAA)

A 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§

(Level AAA)

A mechanism for identifying the expanded form or meaning of abbreviations is available.

Success Criterion 3.1.5 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§

(Level AAA)

A 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§

(Level A)

When any user interface component receives focus, it does not initiate a change of context.

Success Criterion 3.2.2 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§

(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§

(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§

(Level AAA)

Changes of context are initiated only by user request or a mechanism is available to turn off such changes.

Success Criterion 3.2.6 Accidental Activation§

(Level A)


Issue 2

Discussion of the issue is available in Issue 65. To file comments on this proposal, please raise new issues for each discrete comment in GitHub.

For single pointer activation, at least one of the following is true:

  • Activation is on the up-event, either explicitly or implicitly as a platform's generic activation/click event;
  • A mechanism is available that allows the user to choose the up-event as an option;
  • Confirmation is provided, which can dismiss activation;
  • Activation is reversible;
  • Down-event activation event is essential and waiting for the up-event would invalidate the activity.

Guideline 3.3 Input Assistance§

Help users avoid and correct mistakes.

Success Criterion 3.3.1 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§

(Level A)

Labels or instructions are provided when content requires user input.

Success Criterion 3.3.3 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 3.3.5 Help§

(Level AAA)

Context-sensitive help is available.

Success Criterion 3.3.6 Error Prevention (All)§

(Level AAA)

For Web pages that require the user to submit information, at least one of the following is true:

Submissions are reversible.
Data entered by the user is checked for input errors and the user is provided an opportunity to correct them.
A mechanism is available for reviewing, confirming, and correcting information before finalizing the submission.

Principle 4. Robust §

Content must be robust enough that it can be interpreted 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§

(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.


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§

(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.


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.

5. Conformance§

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

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 Conformance Requirements§

In order for a Web page to conform to WCAG 2.1, all of the following conformance requirements must be satisfied:

5.1.1 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.

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.

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.

5.1.2 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.

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.

Authors of Web pages that cannot conform due to content outside of the author's control may consider a Statement of Partial Conformance.

5.1.3 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.

5.1.4 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.)

5.1.5 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:

  1. when any technology that is not relied upon is turned on in a user agent,
  2. when any technology that is not relied upon is turned off in a user agent, and
  3. 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.

5.1.6 §

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.

5.2 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.

5.2.1 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:

  1. Date of the claim
  2. Guidelines title, version and URI "Web Content Accessibility Guidelines 2.1 at https://www.w3.org/TR/WCAG21/" In WCAG 2.0 this was a dated URI, which may need to be adjusted when this becomes a Rec.
  3. Conformance level satisfied: (Level A, AA or AAA)
  4. 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.

    The Web pages may be described by list or by an expression that describes all of the URIs included in the claim.

    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.

  5. A list of the Web content technologies relied upon.

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.

5.2.2 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.
  • 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.

Refer to Understanding Conformance Claims for more information and example conformance claims.

Refer to Understanding Metadata for more information about the use of metadata in conformance claims.

5.3 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:

  1. 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;


  2. 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:

    1. It is not content that is under the author's control.
    2. 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.)

5.4 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§


shortened form of a word, phrase, or name where the abbreviation has not become part of the language

This includes initialisms and acronyms where:

  1. initialisms are shortened forms of a name or phrase made from the initial letters of words or syllables contained in that name or phrase

    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.

  2. 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.

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):

  1. 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,


  2. 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:

    1. The technology is supported natively in widely-distributed user agents that are also accessibility supported (such as HTML and CSS);


    2. The technology is supported in a widely-distributed plug-in that is also accessibility supported;


    3. 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;


    4. 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.

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".)

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.

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.

When citing Web content technologies that have multiple versions, the version(s) supported should be specified.

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

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.


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

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).

Assistive technologies often communicate data and messages with mainstream user agents by using and monitoring APIs.

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.

the technology of sound reproduction

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

Audio description of video provides information about actions, characters, scene changes, on-screen text, and other visual content.

In standard audio description, narration is added during existing pauses in dialogue. (See also extended audio description.)

Where all of the video information is already provided in existing audio, no additional audio description is necessary.

Also called "video description" and "descriptive narration."


a time-based presentation that contains only audio (no video and no interaction)


switch back and forth between two visual states in a way that is meant to draw attention

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


initialism for "Completely Automated Public Turing test to tell Computers and Humans Apart"

CAPTCHA tests often involve asking the user to type in text that is displayed in an obscured image or audio file.

A Turing test is any system of tests designed to differentiate a human from a computer. It is named after famed computer scientist Alan Turing. The term was coined by researchers at Carnegie Mellon University. [CAPTCHA]


synchronized visual and/or text alternative for both speech and non-speech audio information needed to understand the media content

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.

Closed Captions are equivalents that can be turned on and off with some players.

Open Captions are any captions that cannot be turned off. For example, if the captions are visual equivalent images of text embedded in video.

Captions should not obscure or obstruct relevant information in the video.

In some countries, captions are called subtitles.

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:

  1. user agent;
  2. viewport;
  3. focus;
  4. content that changes the meaning of the Web page.

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.


satisfying all the requirements of a given standard, guideline or specification

conforming alternate version

version that

  1. conforms at the designated level, and
  2. provides all of the same information and functionality in the same human language, and
  3. is as up to date as the non-conforming content, and
  4. for which at least one of the following is true:

    1. the conforming version can be reached from the non-conforming page via an accessibility-supported mechanism, or
    2. the non-conforming version can only be reached from the conforming version, or
    3. the non-conforming version can only be reached from a conforming page that also provides a mechanism to reach the conforming version

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.

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).

If multiple language versions are available, then conforming alternate versions are required for each language offered.

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.

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.

Alternate versions should not be confused with supplementary content, which support the original page and enhance comprehension.

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

Clear labels can act as context-sensitive help.

contrast ratio

(L1 + 0.05) / (L2 + 0.05), where

Contrast ratios can range from 1 to 21 (commonly written 1:1 to 21:1).

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.

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.

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.

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.

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 which cannot be determined by content authors).

easily available (or easily available mode or setting)


one or more of the following are true:

  • can be set one time with as wide a scope as possible (such as using the standards of the operating system, from ISO 9241-112 [[ISO_9241-112]] or GPII [GPII] when available)
  • has the option to save or change the setting, where available interoperably, but also for the scope of the set of web pages
  • is reachable from each screen where it may be needed, and the path and the control conforms to all of this document

a sudden, unexpected situation or occurrence that requires immediate action to preserve health, safety, or property


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

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.


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

See general flash and red flash thresholds for information about types of flash that are not allowed.

See also blinking.


processes and outcomes achievable through user action

general flash and red flash thresholds

a flash or rapidly changing image sequence is below the threshold (i.e., content passes) if any of the following are true:

  1. there are no more than three general flashes and / or no more than three red flashes within any one-second period; or
  2. 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


  • A general flash is defined as a pair of opposing changes in relative luminance of 10% or more of the maximum relative luminance where the relative luminance of the darker image is below 0.80; and where "a pair of opposing changes" is an increase followed by a decrease, or a decrease followed by an increase, and
  • A red flash is defined as any pair of opposing transitions involving a saturated red.

Exception: Flashing that is a fine, balanced, pattern such as white noise or an alternating checkerboard pattern with "squares" smaller than 0.1 degree (of visual field at typical viewing distance) on a side does not violate the thresholds.

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.)

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.

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]

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

See also sign language.


phrase whose meaning cannot be deduced from the meaning of the individual words and the specific words cannot be changed without losing the meaning

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

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.


for information purposes and not required for conformance

input error

information provided by the user that is not accepted

This includes:

  1. Information that is required by the Web page but omitted by the user
  2. Information that is provided by the user but that falls outside the required data format or values

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

A keyboard interface allows users to provide keystroke input to programs even if the native technology does not contain a keyboard.

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.

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.


text or other component with a text alternative that is presented to a user to identify a component within Web content

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.

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

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.

Font size is the size when the content is delivered. It does not include resizing that may be done by a user.

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.

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.

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


information captured from a real-world event and transmitted to the receiver with no more than a broadcast delay

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.

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

This definition is based on the International Standard Classification of Education [ UNESCO].


process or technique for achieving a result

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.

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)

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.


text by which software can identify a component within Web content to the user

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.

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

This includes ASCII Art (which is a pattern of characters), emoticons, leetspeak (which uses character substitution), and images representing text


required for conformance

One may conform in a variety of well-defined ways to this document.

on a full-screen window

on the most common sized desktop/laptop display with the viewport maximized

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.


stopped by user request and not resumed until requested by user


information that is not live


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

This definition is based on the International Standard Classification of Education [ UNESCO].


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

Determined in a markup language from elements and attributes that are accessed directly by commonly available assistive technology.

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.

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

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).


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

For the sRGB colorspace, the relative luminance of a color is defined as L = 0.2126 * R + 0.7152 * G + 0.0722 * B where R, G and B are defined as:

  • if RsRGB <= 0.03928 then R = RsRGB/12.92 else R = ((RsRGB+0.055)/1.055) ^ 2.4
  • if GsRGB <= 0.03928 then G = GsRGB/12.92 else G = ((GsRGB+0.055)/1.055) ^ 2.4
  • if BsRGB <= 0.03928 then B = BsRGB/12.92 else B = ((BsRGB+0.055)/1.055) ^ 2.4

and RsRGB, GsRGB, and BsRGB are defined as:

  • RsRGB = R8bit/255
  • GsRGB = G8bit/255
  • BsRGB = B8bit/255

The "^" character is the exponentiation operator. (Formula taken from [sRGB] and [ IEC-4WD]).

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.

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).

Tools are available that automatically do the calculations when testing contrast and flash.

A MathML version of the relative luminance definition is available.

relied upon (technologies that are)

the content would not conform if that technology is turned off or is not supported


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

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


A self-contained portion of written content that deals with one or more related topics or thoughts

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

Different language versions would be considered different sets of Web pages.

Example: A publication 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.

Example: A publication 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.

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

True sign languages are independent languages that are unrelated to the spoken language(s) of the same country or region.

single pointer activation


One point of contact with the screen (vs. multi-touch). A pointer can be any point of contact on the screen made by a mouse cursor, pen, touch (including multi-touch), or other pointing input device. This model makes it easier to write sites and applications that work well no matter what hardware the user has. For scenarios when device-specific handling is desired, this specification also defines properties for inspecting. Pointer Events (REC)Pointer Events Level 2 (ED)

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.

  1. The way the parts of a Web page are organized in relation to each other; and
  2. The way a collection of Web pages is organized
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

technology (Web content)

mechanism for encoding instructions to be rendered, played or executed by user agents

As used in these guidelines "Web Technology" and the word "technology" (when used alone) both refer to Web Content Technologies.

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.

Some common examples of Web content technologies include HTML, CSS, SVG, PNG, PDF, Flash, and JavaScript.


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.

Refer to Understanding Text Alternatives for more information.



The activation of a component when the trigger stimulus is released. On different platforms the "up-event" may be called different things, such as "touchend" or "mouseup". Example: For touchscreen interaction, the event is triggered when a finger is lifted from the touchscreen at the end of a tap.

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.


data that is intended to be accessed by users

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

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.

User interface components include form elements and links as well as components generated by scripts.

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."


the technology of moving or sequenced pictures or images

Video can be made up of animated or photographic images, or both.


a time-based presentation that contains only video (no audio and no interaction)


object in which the user agent presents content

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.

This definition is based on User Agent Accessibility Guidelines 1.0 Glossary.

visually customized

the font, size, color, and background can be set

Web page

a non-embedded resource obtained from a single URI using HTTP plus any other resources that are used in the rendering or intended to be rendered together with it by a user agent

Although any "other resources" would be rendered together with the primary resource, they would not necessarily be rendered simultaneously with each other.

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.

A. Acknowledgments§

Additional information about participation in the Web Content Accessibility Guidelines Working Group (WCAG WG) can be found on the Working Group home page.

A.1 Participants of the WCAG WG active in the development of this document:§

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, Jonas Jacek, Ian Jacobs, Phill Jenkins, 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 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§

Key words for use in RFCs to Indicate Requirement Levels. S. Bradner. IETF. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119
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: https://www.w3.org/TR/WCAG20/
CSS Values and Units Module Level 3. Tab Atkins Jr.; Elika Etemad. W3C. 29 September 2016. W3C Candidate Recommendation. URL: https://www.w3.org/TR/css-values-3/

B.2 Informative references§

The CAPTCHA Project. Carnegie Mellon University. URL: http://www.captcha.net/
Global Public Inclusive Infrastructure. URL: http://gpii.net/
Independent Analysis of the ITC Photosensitive Epilepsy Calibration Test TapeHarding G. F. A.; Binnie, C.D..2002.
IEC/4WD 61966-2-1: Colour Measurement and Management in Multimedia Systems and Equipment - Part 2.1: Default Colour Space - sRGBMay 5, 1998.
Understanding WCAG 2.0. Michael Cooper; Andrew Kirkpatrick; Joshue O Connor et al. W3C. 7 October 2016. W3C Note. URL: https://www.w3.org/TR/UNDERSTANDING-WCAG20/
International Standard Classification of Education. 1997. URL: http://www.unesco.org/education/information/nfsunesco/doc/isced_1997.htm
Web Content Accessibility Guidelines 1.0. Wendy Chisholm; Gregg Vanderheiden; Ian Jacobs. W3C. 5 May 1999. W3C Recommendation. URL: https://www.w3.org/TR/WAI-WEBCONTENT
Techniques for WCAG 2.0. Michael Cooper; Andrew Kirkpatrick; Joshue O Connor et al. W3C. 7 October 2016. W3C Note. URL: https://www.w3.org/TR/WCAG20-TECHS/
A Standard Default Color Space for the Internet - sRGB, Version 1.10. M. Stokes; M. Anderson; S. Chandrasekar; R. Motta.November 5, 1996. URL: http://www.w3.org/Graphics/Color/sRGB.html