Principle 4 - Robust

Robust: Content must be robust enough that it can be interpreted reliably by a wide variety of user agents, including assistive technologies.

Guideline 4.1 - Compatible
Maximize compatibility with current and future agents, including assistive technologies.

• 4.1.1 - Parsing [A]
  In content implemented using markup languages, elements have complete start and end tags, elements are nested according to their specifications, elements do not contain duplicate attributes, and any IDs are unique, except where the specifications allow these features. Understanding 4.1.1

• 4.1.2 - Name, Role, Value [A]
  For all user interface components (including but not limited to: form elements, links and components generated by scripts), the name and role can be programmatically determined; states, properties, and values that can be set by the user can be programmatically set; and notification of changes to these items is available to user agents, including assistive technologies. Understanding 4.1.2