A pioneer in the field of IT accessibility is the United States of America. The World Wide Web Consortium (W3C) has authored a comprehensive work to improve the accessibility of websites using the Web Content Accessibility Guidelines (WCAG).

The first version of WCAG was already published in 1999. Considering these guidelines should make web applications more accessible and accessible to people with disabilities.

As part of WCAG, the W3C has developed the four principles of visibility, usability, intelligibility and robustness. These were taken over, inter alia, in the above-mentioned BITV. Twelve defined guidelines serve as targets for what users should work towards to achieve accessibility as far as possible.

In addition, testable success criteria are defined to obtain the result of the policies implemented. There are three levels of conformity. It should be noted, however, that the highest level of compliance can not provide complete accessibility for humans with all types, manifestations, or combinations of impairments.

More information can be found here.