HTML and CSS Reference
Each guideline is subdivided into checkpoints that serve as the basis for checking WCAG conformance. There are
65 checkpoints, each of which has a priority from 1 to 3. As you will see in the next section, they are very similar to the
conformance levels introduced in WCAG 2.0. The three priority levels are the following:
• Priority 1 ( cf. Level A conformance) : Developers must satisfy these requirements, or else one or
more groups cannot access the content.
• Priority 2 ( cf. Level AA (Double-A) conformance : Developers should satisfy these requirements;
otherwise, the content will be difficult to access for some groups. This level removes
• Priority 3 ( cf. Level AAA (Triple-A) conformance : Developers may address these checkpoints in
order to maximize accessibility.
The second version of the Web Content Accessibility Guidelines (WCAG 2.0) became a W3C Recommendation in
2008 . WCAG 2.0 can be summarized with twelve guidelines following four principles :
Principle 1: User interface components and published information perceivable to anyone.
Alternate text must be provided for nontext contents, making it possible to change it into
Time-based media must have alternatives.
Web content must be available through different presentations without losing information
Both visual and aural contents must be easy to distinguish.
Principle 2: Operable user interface and usable navigation.
All functionality must be available from the keyboard.
Users cannot be forced to perform actions within time limits.
Designs that might cause seizures must be avoided.
Guidance and help must be provided for users to navigate through the site.
Principle 3: Understandable content and operation of the user interface.
Text content must be convenient to read and easy to understand.
Content appearance and operation must be predictable.
Assistance must be provided for users to avoid, find, and correct mistakes.
Principle 4: Robust content with high interoperability that can be used reliably on any kind of user agent,
including assistive technology.
Compatibility must be maximized with current and future user agents and assistive
technology, including the ones running on limited resources .