Understanding WCAG 2.0

A guide to understanding and implementing Web Content Accessibility Guidelines 2.0

Public Editors' Draft 7 January 2014

This version:
Latest version:
Previous version:
Michael Cooper, W3C
Andrew Kirkpatrick, Adobe Systems Inc.
Joshue O Connor, NCBI Centre for Inclusive Technology (CFIT)
Previous Editors:
Loretta Guarino Reid (until May 2013 while at Google, Inc.)
Gregg Vanderheiden (until May 2013 while at Trace R&D Center, University of Wisconsin-Madison)
Ben Caldwell (until September 2010 while at Trace R&D Center, University of Wisconsin-Madison)
Wendy Chisholm (until July 2006 while at W3C)
John Slatin (until June 2006 while at Accessibility Institute, University of Texas at Austin)

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This document, "Understanding WCAG 2.0," is an essential guide to understanding and using Web Content Accessibility Guidelines (WCAG) 2.0 [WCAG20]. It is part of a series of documents that support WCAG 2.0. Please note that the contents of this document are informative (they provide guidance), and not normative (they do not set requirements for conforming to WCAG 2.0). See Web Content Accessibility Guidelines (WCAG) Overview for an introduction to WCAG, supporting technical documents, and educational material.

WCAG 2.0 establishes a set of Success Criteria to define conformance to the WCAG 2.0 Guidelines. A Success Criterion is a testable statement that will be either true or false when applied to specific Web content. "Understanding WCAG 2.0" provides detailed information about each Success Criterion, including its intent, the key terms that are used in the Success Criterion, and how the Success Criteria in WCAG 2.0 help people with different types of disabilities. This document also provides examples of Web content that meet the success criterion using various Web technologies (for instance, HTML, CSS, XML), and common examples of Web content that does not meet the success criterion.

This document indicates specific techniques to meet each Success Criterion. Details for how to implement each technique are available in Techniques for WCAG 2.0, but "Understanding WCAG 2.0" provides the information about the relationship of each technique to the Success Criteria. Techniques are categorized by the level of support they provide for the Success Criteria. "Sufficient techniques" are sufficient to meet a particular Success Criterion (either by themselves or in combination with other techniques), while other techniques are advisory and therefore optional. None of the techniques are required to meet WCAG 2.0, although some may be the only known method if a particular technology is used. "Advisory techniques" are not sufficient to meet the Success Criteria on their own (because they are not testable or provide incomplete support) but it is encouraged that authors follow them when possible to provide enhanced accessibility.

In addition to techniques for addressing the success criteria, "Common Failures" are also documented. These "Common Failures" are authoring practices that are known to cause Web content to fail to conform to WCAG 2.0. Authors must avoid those practices in order to meet the WCAG 2.0 Success Criteria.

This document is part of a series of documents published by the W3C Web Accessibility Initiative (WAI) to support WCAG 2.0. This document was published as a Working Group Note at the same time WCAG 2.0 was published as a W3C Recommendation. Unlike WCAG 2.0, is expected that the information in Understanding WCAG 2.0 will be updated from time to time. See Web Content Accessibility Guidelines (WCAG) Overview for an introduction to WCAG, supporting technical documents, and educational material.

Status of This Document

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

This is a Public Editors' Draft of "Understanding WCAG 2.0". The Web Content Accessibility Guidelines Working Group considers this document to be important for understanding the success criteria in the Web Content Accessibility Guidelines (WCAG) 2.0 Recommendation. Please note that the contents of this document are informative (they provide guidance), and not normative (they do not set requirements for conforming to WCAG 2.0).

Understanding WCAG 2.0 was previously published on 11 December 2008 as a Working Group Note and updated 14 October 2010, 3 January 2012, and 5 September 2013. This new version updates the support information provided for WCAG 2.0. Note that WCAG 2.0 itself remains unchanged, only the informative support materials have been updated. Primary changes include new techniques and clarifications based on input from the public and translators. The purpose of this draft is to collect public feedback on proposed changes since the Understanding WCAG 2.0 Working Group Note of 5 September 2013. The Working Group intends to publish an updated Note once feedback from this review has been incorporated. The existing Understanding document remains in place as a W3C Note while this separate draft update is under review and the WCAG Working Group addresses comments. The Working Group is still discussing whether it is appropriate to use various aria attributes to provide text alternatives for images without providing an alt attribute. ARIA10: Using aria-labelledby to provide a text alternative for non-text content (ARIA) is included to invite public comment and help the working group come to a conclusion about this technique as well as related items (e.g. F65: Failure of Success Criterion 1.1.1 due to omitting the alt attribute on img elements, area elements, and input elements of type "image"). Examples within ARIA10 demonstrate situations where it might be desirable just to use aria-labelledby with no alt attribute. We solicit feedback on this example and on the general issue. The changes are highlighted in the diff-marked version.

Comments on this draft are due on or before 14 February 2014. The Working Group requests that any comments be made using the provided online comment form. If this is not possible, comments can also be sent to public-comments-wcag20@w3.org. The archives for the public comments list are publicly available. Comments received on this document may be addressed in future versions of this document, or in another manner. Archives of the WCAG WG mailing list discussions are also publicly available, and future work undertaken by the Working Group may address comments received on this document.

This document has been produced as part of the W3C Web Accessibility Initiative (WAI). The goals of the WCAG Working Group are discussed in the WCAG Working Group charter. The WCAG Working Group is part of the WAI Technical Activity.

Publication as a Public Editors' 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.

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