HTML 5 Tutorial and Reference
Differences between HTML 4 and HTML 5
FAQs about HTML 5 along with answers
HTML Definitions
Polyglot HTML Documents
You may notice that, when there is a difference between the two possible flavors of HTML 5 syntax, rather than confusing things by presenting examples using both possible options, the syntax that is shown is one that could be used for documents that could be rendered by HTML browsers that interpreting the input in either way. These are known as Polyglot HTML Documents.