The W3C Web Accessibility Initiative Standard (WAI) is a set of guidelines that have been devised by the W3C to assist developers and lawmakers in the task of enforcing website accessibility.
Most accessibility legislation throughout the world directly follows the official Web Accessibility Initiative Standard , specifying the documents and the version number; others have written their own versions or combined these with general usability or best practices guidelines. An excellent and current source for legislation and guidelines in different countries can be found at Visit the W3C Website at www.w3.org (n.b. external link).
W3C recommendation, Web Content Accessibility Guidelines 1.0 became a W3C recommendation May 5, 1999 and explains accessible use of Web technologies for page authors and site developers. It has three priority levels and three conformance levels, 14 guidelines, and over 60 checkpoints all of which can be found at their website.