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This section is informative.
A user agent is any software that retrieves and presents Web content for end users. Examples include Web browsers, media players, plug-ins, and other programs including assistive technologies, that help in retrieving, rendering and interacting with Web content. This document specifies requirements that, if satisfied by user agent developers, will lower barriers to accessibility.
Accessibility involves a wide range of disabilities, including visual, auditory, physical, speech, cognitive, language, learning, neurological disabilities, and disabilities related to ageing. This document emphasizes the goal of ensuring that users, including users with disabilities, have control over their environment for accessing the Web. Key methods for achieving that goal include:
Some users may have more than one disability, and the needs of different disabilities may contradict. Thus, many of the requirements in this document involve configuration as one way to ensure that a functionality designed to improve accessibility for one user does not interfere with accessibility for another. A default user agent setting may be useful for one user but interfere with accessibility for another, therefore this document prefers configuration requirements rather than requirements for default settings. For some content, a feature required by this document may be ineffective or cause content to be less accessible, making it imperative that the user be able to turn off the feature. To avoid overwhelming users with an abundance of configuration options, this document includes requirements that promote ease of configuration and documentation of accessibility features. [Ed Note: One sentence summarizing device independence, spatial independence, and temporal independence needed here. ]
This document also acknowledges the importance of author preferences, however, requirements are included to override certain author preferences when the user would not otherwise be able to access that content.
Some of the requirements of this document may have security implications, such as communication through APIs, and allowing programmatic read and write access to content and user interface control. This document assumes that features required by this document will be built on top of an underlying security architecture. Consequently, unless permitted explicitly in a success criterion, this document grants no conformance exemptions based on security issues.
The UAWG expects that software which satisfies the requirements of this document will be more flexible, manageable, extensible, and beneficial to all users.
In order to meet the varying needs of the different audiences using UAAG, several layers of guidance are provided including overall principles, general guidelines, testable success criteria and a rich collection of sufficient techniques, advisory techniques, and documented common failures with examples, resource links and code.
Principles - At the top are five principles that provide the foundation for accessible user agents. Three of the principles are congruent to Web Content Accessibility Guidelines (WCAG) 2.0: perceivable, operable, understandable. Two principles have been added which are specific to user agents: follows specifications and programmatic access.
Guidelines - Under the principles are guidelines. The guidelines provide the basic goals that authors should work toward in order to make user agents more accessible to users with different disabilities. The guidelines are not testable, but provide the framework and overall objectives to help authors understand the success criteria and better implement the techniques.
Success Criteria - For each guideline, testable success criteria are provided to allow UAAG 2.0 to be used where requirements and conformance testing are necessary such as in design specification, purchasing, regulation, and contractual agreements. In order to meet the needs of different groups and different situations, three levels of conformance are defined: A (lowest), AA, and AAA (highest). Additional information on UAAG levels can be found in the section on Conformance.
Sufficient and Advisory Techniques [Ed Note: Are we going to have Advisory Techniques?] - For each of the guidelines and success criteria in the UUAG 2.0 document itself, the working group has also documented a wide variety of techniques. The techniques are informative and fall into two categories: those that are sufficient for meeting the success criteria and those that are advisory. The advisory techniques go beyond what is required by the individual success criteria and allow authors to better address the guidelines. Some advisory techniques address accessibility barriers that are not covered by the testable success criteria. Where common failures are known, these are also documented. See the section on UAAG Supporting Documents for more information on Techniques.
All of these layers of guidance (principles, guidelines, success criteria, and sufficient and advisory techniques) work together to provide guidance on how to make user agents more accessible. Developers are encouraged to view and apply all layers that they are able to, including the advisory techniques, in order to best address the needs of the widest possible range of users.
Note that even user agents that conform at the highest level (AAA) will not be accessible to individuals with all types, degrees, or combinations of disability, particularly in the cognitive, language, and learning areas. Developers are encouraged to consider the full range of techniques, including the advisory techniques, as well as to seek relevant advice about current best practice to ensure that their user agent is accessible, as far as possible, to this community.
A separate document, entitled "Techniques for User Agent Accessibility Guidelines 2.0" (the "Techniques document" from here on) will be produced at a later date. It will provide suggestions and examples of how each success criteria might be satisfied. It also includes references to other accessibility resources (such as platform-specific software accessibility guidelines) that provide additional information on how a user agent may satisfy each success criteria. The techniques in the Techniques document are informative examples only, and other strategies may be used or required to satisfy the success criteria. The UAWG expects to update the Techniques document more frequently than the current guidelines. Developers, W3C Working Groups, users, and others are encouraged to contribute techniques.
Web accessibility depends not only on accessible user agents, but also on the availability of accessible content, a factor that is greatly influenced by the accessibility of authoring tools. For an overview of how these components of Web development and interaction work together, see:
User Agents may claim conformance to UAAG 2.0 at one of three conformance levels. The level achieved depends on the level of the success criteria that have been satisfied. The conformance levels are:
Any software that retrieves and presents Web content for end users. Examples include Web browsers, media players, plug-ins, and other programs including assistive technologies, that help in retrieving, rendering and interacting with Web content.