Need help finding the right HTML5 element or attribute for your web page or application? HTML5 Pocket Reference is the classic reference that web designers and developers have been keeping close at hand for more than thirteen years. This fifth edition has been updated to reflect the current state of HTML5, including the HTML5 Candidate Recommendation, the emerging HTML5.1 Working Draft, and the living WHATWG standard. Features
This is an exhaustive and definitive documentation for HTML5 and I really like it. Every element and attribute is listed, defined and there are also examples of them.
The second most used book is the CSS pocket reference, and the first is one I made myself - a notebook where I keep all the niggly things I'm CONSTANTLY having to look up; things like the ascii code for é, and the difference between "display:none" and "visibility:hidden" (a CSS reference). You can't publish a book like that.
The HTML pocket reference goes with me on work trips, because the big version is just too big.
With the proliferation of smartphones, I can't imagine any 'Pocket Reference' being indispensable. This one contains some good information, but nothing you can't find online or in a more comprehensive book.