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This section is informative.

You are reading the Web Content Accessibility Guidelines (WCAG) version 2.0. This is the central document that defines the requirements for making Web content accessible to a wide range of people with disabilities, including blindness and low vision, deafness and hearing loss, learning difficulties, cognitive limitations, limited movement, speech difficulties, and others. Following these guidelines will also make your Web content more usable to many other users, including older users. It will also enable people to access Web content using many different devices - including a wide variety of assistive technologies and mobile technologies.

WCAG 2.0 covers a wide range of recommendations for making Web content more accessible. The guidelines do not include standard usability recommendations except where they have specific impact on accessibility.

The WCAG 2.0 document itself consists of:

Related Documents

In addition to WCAG 2.0 (this document) there are a number of related support documents that provide additional information and examples. These other documents are informative only and do not define conformance to WCAG 2.0. Only this document (WCAG 2.0) is normative. That is, only this document can be used for determining conformance to these guidelines. Readers should consult WCAG 2.0 in order to determine the exact wording of the success criteria and for information about documenting conformance.

The other documents in this set are provided to help readers understand WCAG 2.0 and how to produce conforming content. These informative documents are written to be used by a diverse audience, including but not limited to:

Currently, these informative documents include:

The Working Group plans to publish a number of other technology-specific techniques documents and encourages development of techniques documents that show how to meet WCAG 2.0 using non-W3C technologies. Please visit the Working Group home page for a complete list of these and other informative documents related to WCAG 2.0.

Every attempt has been made to make WCAG 2.0 and the related documents listed above as readable and usable as possible while retaining the accuracy and clarity needed in a technical specification. Sometimes technical terms are needed for clarity or testability. In these cases, the terms are defined in Appendix A: Glossary . To assist readers, there is a How to Meet link beside every success criterion that puts readers one click away from detailed information on that success criterion and two clicks away from the specific technique descriptions related to the success criterion.

The Working Group recognizes that readers who are new to accessibility may need or want additional information. For these readers, the work of the Web Accessibility Initiative and its Education and Outreach Working Group is highly recommended. The articles called Getting Started: Making a Web Site Accessible and How People with Disabilities Use the Web are especially useful.

Authoring tools

A large part of Web content is created using authoring tools. These tools often determine how Web content is implemented, either by making authoring decisions directly or by limiting the choices available to the author. As a result, authoring tools will play an important role in creating Web content that conforms to the Web Content Accessibility Guidelines. At the same time, we recommend that all authors become familiar with the Guidelines because this will help in creating accessible content and coverage of the Guidelines may vary between tools.

Developers of authoring tools can make their tools aware of the Web Content Accessibility Guidelines by following the Authoring Tool Accessibility Guidelines. The working group encourages users and purchasers of authoring tools to consider conformance to the Authoring Tool Accessibility Guidelines as a criterion when selecting tools. The current version at WCAG 2.0's release is Authoring Tool Accessibility Guidelines 1.0. However, version 2.0 is nearing completion and it is based on WCAG 2.0. The latest version of the Authoring Tool Accessibility Guidelines 2.0 can be found at http://www.w3.org/TR/ATAG20.

The Role of User Agents

Web content is always rendered by a user agent. A user agent is any software that retrieves and renders Web content for users and includes assistive technologies. Web content that conforms to WCAG 2.0 is most likely to be rendered correctly by user agents that conform to the User Agent Accessibility Guidelines (UAAG). For more information about the relationship between WCAG 2.0 and other WAI accessibility guidelines, see Essential Components of Web Accessibility.

The Four Principles of Accessibility

The WCAG 2.0 Guidelines are organized around the following four principles:

  1. Content must be perceivable

  2. Interface components in the content must be operable

  3. Content and controls must be understandable

  4. Content should be robust enough to work with current and future user agents (including assistive technologies)

These four principles lay the foundation necessary for anyone to access and use Web content. WCAG 2.0 offers information about how to increase the ability of people with disabilities to perceive, operate, and understand Web content. Under each principle there is a list of guidelines that address the principle. Under each guideline there are success criteria used to evaluate conformance to this standard for that guideline. The success criteria are written as statements that will be either true or false when specific Web content is tested against the success criteria. The success criteria are grouped into three levels of conformance, each representing a higher level of accessibility for that guideline.

The principles, guidelines, and success criteria represent concepts that address accessibility issues and needs, regardless of the technology used. They are not specific to HTML, XML, or any other technology. This approach makes it possible to apply WCAG 2.0 to a variety of situations and technologies, including those that do not yet exist.

The principles and guidelines give direction and guidance to Web authors. The success criteria are written as true/false statements so that they can be used in determining conformance. Only the success criteria are testable.

Important New Terms Used in WCAG 2.0

WCAG 2.0 includes several important new terms. These terms are defined in the Glossary ( Appendix A: Glossary ), and links to the definitions are provided whenever these and other important terms are used in the success criteria. The terms are introduced briefly here to make this new vocabulary easier to understand.

"Web unit" is one of these important new terms. Web pages are the most common type of Web unit. The broader term was chosen because it covers Web applications and other types of content to which the word "page" may not apply. A Web unit is any collection of information, consisting of one or more resources, intended to be rendered together, and identified by a single Uniform Resource Identifier (such as a URL). For example, A Web page containing several images and a style sheet is a typical Web unit.

Several success criteria require that content (or certain aspects of content) can be "programmatically determined." This means that the author is responsible for ensuring that the content is delivered in such a way that software can access it. This is important in order to allow assistive technologies to recognize it and present it to the user, even if the user requires a different sensory modality than the original. For example, some assistive technologies convert text into speech or braille. This will also allow content in the future to be translated into simpler forms for people with cognitive disabilities, or to allow access by other agent based technologies. This can happen only if the content itself can be programmatically determined.

WCAG 2.0 also introduces the term "baselineā€ which allows WCAG 2.0 to adapt to changing technologies and to the needs of different countries and environments. Baselines are described in more detail in the conformance section and in About Baselines for WCAG 2.0.