Thanks for asking.
Obviously, it's about HTML in general and HTML5 in particular. It's also about how to think about, plan, design and develop for the Web.
I tried to write it so that it would be understandable by content creators and editors – People who are using the Web to publish rich content using services that allow some HTML markup, such as: Google Docs, Blogs, eBay and Wikipedia. But, there's also a chapter on building websites from scratch.
Mostly though, I've tried to provide guidance based on my 17 years of developing Web sites for individuals, small businesses and organizations.
You'll find links to other material, including a sample chapter, on my website at:
http://LarryAronson.com/2010/html-manual-of-style/
I hope that you'll find the information useful and enjoyable.
Larry