The best instruction books don’t just tell you how to do something, or why things are done a certain way, they are forward looking to how things will likely be done in the future, educated guesses backed up with facts. With HTML5 Guidelines, Klaus Förster and Bernd Öggl have put together a set of 12 chapters on different technologies that are under development for the HTML5 standard. As the book says numerous times, the standard is evolving and while some parts, like <canvas> are already widely supported, others like MathML are not yet, and others like <video> and geo-location are still being hashed out and consistent behaviour across browsers can not be assumed.
The book starts off with a bit of history of how HTML5 came out of the failure of XHTML2 to gain acceptance and the desire for HTML4.1 to continue to be developed rather than be extended willy-nilly by browser makers, an outcome that at worst would be like returning back to the days when Netscape and Microsoft played one-up with each other extending HTML in incompatible ways.
The chapters in the book cover: Structure and semantics for documents, Intelligent forms, Video and audio, Canvas, SVG and MathML, Geolocation, Web storage and offline web applications, WebSockets, Web Workers, Microdata and other improvements.
The chapter on the <canvas> element is particularly in-depth and that's partly because <canvas> is one of the best supported HTML5 features. On the other hand, the HTML5 <video> mess is addressed with examples of how to support H.264, WebM and Theora video in a compatible ways. Since the best selling tablet today only supports H.264, there's some good information for developers who will need to support it as well as newer Android tablets coming only the market.
While the audio and visual features get a lot of attention, HTML5 promises to improve the web experience and make it possible to mimic traditional desktop applications. Among these improvements are better form elements, off-line storage, geo-location and some general improvements like spell-checking and drag and drop files. Those last two are already part of Firefox and Chrome, but this aims to standardize them.
In closing, this is a good solid book on how to use HTML5 as it exists today. The 12 chapters that make up the book cover most of what developers have available to them today. To borrow William Gibson's best-known quote, HTML5 is here it's just not completely supported in one place; or in other words, the features that will probably be part of HTML5 are support today in different browsers, but no one browser supports them all. This book will help you navigate through that fact.