a user agent that:
provides services beyond those offered by the host user agents to meet the requirements of users with disabilities. Additional services include alternative renderings (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).
relies on services provided by one or more other "host" user agents. Assistive technologies communicate data and messages with host user agents by using and monitoring.APIs.
Note: In this definition the host user agents are user agents in the general sense of the term. The output of host user agents may not be easily read by any humans, but it may provide important services to assistive technologies like retrieving Web content from program objects or parsing markup into identifiable bundles.
Example: Examples of assistive technologies that are important in the context of this document include the following:
screen magnifiers, which are used by people with visual disabilities to enlarge and change colors on the screen to improve the visual readability of rendered text and images;
screen readers, which are used by people who are blind or have reading disabilities to read textual information through synthesized speech or braille displays;
voice 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;
alternative pointing devices, which are used by people with certain physical disabilities to simulate mouse pointing and button activations.
Note: This definition is based on User Agent Accessibility Guidelines 1.0 Glossary.