Accessibility refers to the ability to access to the Web and their content by all persons regardless of their disabilities (physical, intellectual or technical) or because of difficultes that arise out of the context of use (technological or environmental). This quality is closely related to the usability.
When the web sites are designed in accessibility, all users can access on equal conditions to the contents. For example, when a site has a XHTML code semantically correct, provides a text alternative to the pictures, and links are given a meaningful name, this allows the blind users to read the contents using screen readers or Braille lines. When the videos have subtitles, users with hearing impairments may understand them fully. If the contents are written in simple language and illustrated with diagrams and animations, users with dyslexia or learning difficulties are also in a better position to understand them.
If the size of the text is large enough, users with visual impairments can read it without difficulty. Similarly, a suitable size of buttons or active areas can facilitate its use to users who cannot control the mouse accurately. If you avoid actions that depend on a particular device (pressing a key, click with the mouse) the user may choose the device that best suits him.
The limitations in the accessibility of Web sites can be:
Patterns of Web accessibility
The highest body within the hierarchy on the internet that is responsible for promoting the accessibility is the World Wide Web Consortium (W3C), in particular its working group Web Accessibility Initiative (WAI). In 1999, the WAI published version 1.0 of their patterns of Web accessibility. With the passage of time it has become a benchmark internationally accepted. In December 2008 WCAG 2.0 were adopted as official recommendation. These guidelines are divided into three blocks: