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.
4.3.1.Specific implementation measures
- 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.