Accessibility is in ISO / TS 16071 (ISO, 2003) an extension of usability: "Accessibility is the usability of a product, a service, an environment or a building for people with the greatest variation of skills".
The following principles are taken from a draft revision of the Guidelines for Software Accessibility (ISO, 2003):
All users have equal rights and can use all of the application features.
The application takes account of a wide range of user abilities and needs.
The application provides information to the user in a manner that is discernible for him/her.
The application provides information to the user in a manner that he/she can understand.
The operator controls of the application can be operated by all users, taking account of a wide range of user skills.
- Fault tolerance
The application prevents as far as possible risks and adverse consequences of unintended user actions.
- Robust technologies
The application uses robust and standardized technologies, for maximum interoperability with tools and auxiliary programs used by the user.
- Colors: Color should not be relied on as the only distinguishing criterion (example: red/green color blindness). Corresponding information should always be provided in the form of text information.
- Images should always provide the ALT attribute.
- Operator controls should be accessible not only exclusively via mouse, but also via the keyboard (for example, via the tab key for controlling form elements).
- For videos, transcripts or video subtitles should be provided.
- Sites should offer the opportunity of navigating to the page with keyboard input only ("Skip Navigation").
- Colors: Ensure that there is a sufficient contrast ratio for all fonts and controls.
- For animations, an image sequence that is too fast should be avoided. Always offer the option to pause or disable the motion sequence.
Guidelines for Accessibility for the Web
Currently there are two major movements that coordinate a set of guidelines for accessibility for the web.
- The Web Accessibility Initiative (WAI), which is part of the World Wide Web Consortium (W3C). The WAI developed the Web Content Accessibility Guidelines (WCAG). These guidelines describe how to make websites accessible.
- Section 508 of the US Rehabilitation Act, which is basically a comprehensive set of rules designed to help designers make their web content accessible.
The WCAG provides three compliancy levels: A, AA and AAA. Each level requires a stricter set of conformance guidelines that have to be implemented in order to obtain the respective validation.
This information was written in collaboration with the UX Guide. Daimler UX Guide (internal link – requires authentication)