HTML5 Doctor is the best source information for most HTML5 topics, including the clearest definition of the new outline algorithm I’ve read so far, in this article by Mike Robinson: http://html5doctor.com/outlines/. You can download the element flowchart shown in Figure 2-1 from http://html5doctor.com/resources/#flowchart/. See also Derek Johnson’s article in Smashing Magazine: http://coding.smashingmagazine.com/2011/08/16/html5-and-the-document-outlining-algorithm/.
For much more detail on the HTML5 structural elements problem, I strongly suggest you read Luke Stevens’s book The Truth About HTML5; find it at http://www.truthabouthtml5.com/. If you want to read the full HTML5 specification and make up your own mind, I advise going for the developer’s version at http://developers.whatwg.org/sections.html.
Read the full WAI-ARIA specification at http://www.w3.org/TR/wai-aria/. The Paciello Group Blog is worth reading for information about accessibility in HTML5, and this post on landmark roles is directly relevant: http://www.paciellogroup.com/blog/2010/10/using-wai-aria-landmark-roles/.
Divya Manian’s article on semantics was published by Smashing Magazine at http://coding.smashingmagazine.com/2011/11/11/our-pointless-pursuit-of-semantic-value/. For more on aboutness and the importance of semantics, I highly recommend the book Ambient Findability: What We Find Changes Who We Become by Peter Morville (O’Reilly, 2005). The website http://webdatacommons.org/ provides information and statistics about sites that use structured data.
Read all about microformats at http://microformats.org/. A revision of the syntax, microformats 2.0, was started in 2010 and is still underway; learn more about that at http://microformats.org/wiki/microformats-2.
If you want to learn more about the RDFa format, the W3C published an excellent primer: http://www.w3.org/TR/xhtml-rdfa-primer/.
The best resource for learning about microdata comes from the HTML5 Doctor again: http://html5doctor.com/microdata/. If you’re feeling masochistic and prefer to read the spec in detail, you’ll find it at http://www.w3.org/TR/microdata/.
You can get more information on Schema.org at—wait for it!—http://schema.org/, and Google’s documentation of rich snippets is at http://support.google.com/webmasters/bin/answer.py?hl=en&answer=99170. You’ll find the testing tool at http://www.google.com/webmasters/tools/richsnippets/.
John Resig wrote a concise introduction to data attributes on his blog, http://ejohn.org/blog/html-5-data-attributes/, and the data() method is fully documented on the jQuery website at http://api.jquery.com/data/.