Success Criteria
4.1.1 Parsing
Content must be robust enough that it can be interpreted reliably by a wide variety of user agents, including assistive technologies.
Maximize compatibility with current and future user agents, including assistive technologies.
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.
Note 1: Start and end tags that are missing a critical character in their formation, such as a closing angle bracket or a mismatched attribute value quotation mark are not complete.