The Web Content Accessibility Guidelines(WCAG) are a set of international standards for accessible web interfaces. The Authoring Tool Accessibility Guidelines (ATAG) apply to software used to produce web content, like content management systems and WYSIWYG editors.

Generally, laws require web-based software to meet WCAG level AA standards for the most recent version of the guidelines, currently version 2.1 (released in 2018). Level AAA applies only to specific types of content in certain contexts, like long documents. The standard itself states, “It is not recommended that Level AAA conformance be required as a general policy for entire sites because it is not possible to satisfy all Level AAA Success Criteria for some content.”

Some procurement standards may also specify ATAG compliance.

Note that the guidelines on cognitive accessibility are still in draft, and are due to become part of WCAG in the next major release.

The full WCAG guidelines are very detailed and technical; they were written to be used by both browser vendors and legislative groups. If you are new to accessibility, it's better to start with a more human-readable checklist:

• Deque University Web Accessibility Checklist
• WebAIM WCAG 2 Checklist
• A11y Project Checklist

If you want something more formal, the Section 508 Trusted Tester Conformance Test Process might be right for you.

While ATAG may still be included in your local laws on accessibility, its guidelines are slowly being incorporated into WCAG. (When ATAG and WCAG were originally written, content management systems were exclusively for enterprise work, and it made sense to have a separate set of guidelines for editing interfaces.) Generally speaking, WCAG is the standard to pay attention to.

Always use the most recent version of WCAG, regardless of the version that is specified in your local laws. Legislation is often several years behind reality, and WCAG 2.x versions are written to be backward compatible.

The four principles of accessible web interfaces, POUR, map to the four major sections of WCAG numbering:

“Some people think about Perceivable = visual design, Operable = interaction design, Understandable = content design, Robust=largely dev. This is very rough mapping, though it might help with how you think about it.” – Jennifer X. Zhang, Microsoft