Semantics in HTML 5
The BBC's dropping of hCalendar because of accessibility and usability concerns demonstrates that we have pushed the semantic capability of HTML far beyond what it can handle. The need to clearly and unambiguously add rich, meaningful semantics to markup is a driving goal of the HTML 5 project. Yet HTML 5 has two problems: it is not backward compatible because its semantic elements will not work in 75% of our browsers; and it is not forward compatible because its semantics are not extensible. If “making up new elements” isn't the solution, what is?