Accessibility

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.

Limitations

The limitations in the accessibility of Web sites can be:

• Visual limitations: in its varying degrees, from low vision to complete blindness, in addition to difficulties in distinguishing colors (color blindness). 
• Motor limitations: derived from the difficulty or inability to use the hands, including tremors, slow muscle, etc. due to diseases such as Parkinson's Disease, muscular dystrophy, cerebral palsy, amputations,...
• Auditory limitations: deafness or hearing impairments.
• Cognitive limitations: learning difficulties (dyslexia, dyscalculia) or cognitive disabilities that affect memory, attention, the logical skills, etc.

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:

• Patterns of accessibility to content on the Web (WCAG). They are targeted to webmasters and indicate how to make the contents of the Web site accessible.
• Accessibility Guidelines for authoring tools (ATAG). They are directed to the developers of the software that use webmasters, so that these programs would facilitate the creation of accessible sites.
• Accessibility Guidelines for user agents (UAAG) are targeted to developers of user agents (browsers and similar), with the objective that these programs facilitate all users the access to the web sites.