Jennifer is one of the first webdesigners , she is designing webpages since 1993. She is the author of the widely known Learning Web Design book series. She has written numerous books and pocket references about HTML and XHTML. Her first pocket reference was written in 1999, the second was released in 2002 and these continuously received updates in 2006 and 2009. The newest of these(5th edition) has been published in August 2013.
The book describes the main motivation behind HTML5, how the draft for HTML5 was created, who were the main contributors. The book presents which are the new semantic elements in HTML5 when and how should be these used. There is a section, which I consider very useful, about HTML5 event handlers. Each element and event handler is marked if that has a special behavior and is described what is the difference in certain situations.
Jennifer added information about the new elements which are available in the HTML5.1 draft, she also added some useful tools(online resources) with the help of these you can check if the created HTML5 code is valid or not.
I liked about the book, that is concise, for each element you have described its purpose, the semantic meaning, when and where(after, before, inside which tag) should it be used. Another important thing is, there are a lot of good and meaningful examples in the book which you can inspire from.