The power of the Web is in its universality. Access by everyone regardless of disability is an essential aspect.
— Tim Berners-Lee, W3C Director and inventor of the World Wide Web
Accessibility has recently become a basic or additional legal requirement for many state and governmental websites, bureaus, agencies, schools, academic sites, scientific publications, professionals, and international projects.
Accessible websites assure accessibility to web page graphics by the visually impaired using advanced technologies, e.g., screen readers and refreshable Braille displays. This can be obtained by using text labels and descriptors for graphics and tables in the source code.
However, Web accessibility techniques are not limited to the visually impaired or people with other disabilities. In fact, they also ease mobile access to Web contents and improve overall webpage quality.
More and more countries have introduced legislations addressing the need for websites to be accessible to people with disabilities, or the requirement to be non-discriminative against people with disabilities. Some examples are the Disability Discrimination Act 1992 (Australia), Disability Act, 2005 (Ireland), Disability Discrimination Act 1995 (UK), and Section 508 of the Rehabilitation Act (USA).
Standards and de facto standards
WCAG 1.0 and WCAG 2.0
Web Content Accessibility Guidelines (WCAG) are collections of Web accessibility guidelines published by W3C's Web Accessibility Initiative (WAI).
WCAG 1.0 can be satisfied at three priority levels: Priority Level 1 (requirements that must be satisfied), Priority Level 2 (requirements that should be satisfied), and Priority Level 3 (requirements that may be satisfied). WCAG 2.0 conformance requirements are defined as Level A, Level AA (Double-A), and Level AAA (Triple-A) requirements, respectively.
Unlike most markup and notation codes used on the Web, accessibility cannot be validated automatically. Although there are some useful tools to generate reports on accessible content, this task requires a qualified, experienced web developer. Checkpoints and success criteria have been published by W3C.