level is described as AAA or Triple-A. Version 2 WCAG 2.0 consist of twelve guidelines organized under four principles (websites must be perceivable, operable, understandable, and robust). Each guideline has testable success criteria (61 in all). The W3C's Techniques for WCAG 2.0 is a list of techniques that help authors meet the guidelines and success criteria. The techniques are periodically updated whereas the principles, guidelines and success criteria are stable and do not change. WCAG 2.0 uses the same three levels of conformance (A, AA, AAA) as WCAG 1.0, but has redefined them. The WCAG working group maintains an extensive list of web accessibility techniques and common failure cases for WCAG 2.0. WCAG 2.1 is backwards-compatible with WCAG 2.0, which it extends with a further 17 success criteria. WCAG referenced by law This section only refers to specific instances where WCAG, or a closely related derivative thereof, is specifically codified into law. There are many laws relating to accessibility in general and which may apply to websites, though they don't necessarily refer to WCAG. It is nevertheless considered prudent to follow WCAG guidelines to help protect against potential lawsuits relating to accessibility. United States In 2013, the US Department of Transportation amended the Air Carrier Access Act (ACAA) to require Airlines make their Websites accessible, requiring conformance to WCAG 2.0, meeting Level AA Success Criteria. In January 2017, the US Access Board approved a final rule to update Section 508 of the Rehabilitation Act of 1973. The new rule adopts seventeen WCAG 2.0 success criteria, but 22 of the 38 existing A-level and AA-level criteria were already covered by existing Section 508 guidelines. The rule requires adherence to the new standards twelve months from its date of publication in the federal register. In December, 2021 the 11th circuit court vacated a sometimes-cited case from 2017, which had referred to the WCAG guidelines as "industry standard". The 11th circuit court's ruling rendered the 2017 case moot. As such, the case is no longer citable as caselaw. On March 2, 2022, the 11th circuit court refused to rehear the case. European Union Directive 2016/2102 requires websites and mobile applications of public sector (i.e. government) bodies to conform to WCAG 2.1 Level AA. As of June 2021, the directive covers websites and mobile apps. The European Parliament approved the directive in October 2016, the European Commission updated the WCAG reference from 2.0 to