Some great references of the HTML5 specification online:
For more reference, please check out the course name: HTML5: Structure, Syntax, and Semantics from the link of Lynda.com below.
HTML5: Structure, Syntax, and Semantics gives designers a deeper understanding of HTML5 and shows how to create richer, more meaningful web pages with structural tags and descriptive attributes. Author James Williamson presents an overview of HTML5 and its development, defines the new tags and attributes, and discusses how browsers parse and display HTML5 content. The course also includes step-by-step instructions for constructing an HTML5 document with a header and footer, navigation, content groups, and formatting. Exercise files are included with the course.
Defining basic elements
Exploring the content model
Creating document sections
Using hgroup to override sectioning
Using the proper nesting structure
Choosing the right structural element
Using class and ID attributes
Grouping content with asides
Using divs in HTML5
Creating block level links
Defining link relationships
Understanding current browser support
Adding support for elements in older browsers
Following is a list of known implementations of HTML5 and related features in web browsers.
Implementations in Web browsers
When can I use…
Compatibility tables for support of HTML5, CSS3, SVG and more in desktop and mobile browsers.
How well does your browser support HTML5?
Tutorials and Articles