The purpose of Web Accessibility is to attain universal access to the Web regardless of the software, or the user's device and ability. The Initiative of Web Accessibility began with this purpose, WAI (Web Accesibility Initiative), and it is promoted by the World Wide Web Consortium (W3C).
W3C, intending to make accessibility measurable, developed “Web Content Accessibility Guidelines (WCAG)”, also intended to serve as guidelines for webpage design. They are 14 guidelines with checkpoints, each one related to a priority, so each priority indicates the need to check that point.
Depending on the compliance to these checkpoints, different conformity levels are established: A, AA and AAA.