The text does not discuss all of VirtueMart, but confines itself to only those points related to the front end; ie. what the website visitor directly can see when shopping. The so-called default theme shows a large number of settings that you can readily tweak. These impact points like whether an item for sale is out of stock, whether the customer can write a review of a purchased item, your return policy [usually vital for many commerce sites], and which shopping areas [web pages] of the site need to use https for security, since pages that just use http traverse the Internet as plaintext and can thus be trivially read by any intermediate machine. There are many more items than this, as evidenced by the numerous screen captures in the text, but the previous ones give you some of the flavour of what is available.
4 major template groups are then explained. A lot of the value of the narrative comes in how the functions are described in an understandable manner, and the PHP files that perform each function are listed. This lets you wade through the morass of many PHP files and understand in depth, if you need to, how the functions are implemented. From the programmer's standpoint, it can save much time in providing a top-down guide to the source code. I am guessing from my own experience with open source code, that the text's guide is far superior to what is provided in the in situ documentation.
Perhaps the more advanced section of the book is where it delves into how you can write your own theme, in place of the default theme. The coding here is more advanced and can be more intricate than earlier, if you had gone into changing template group PHP files. Making a theme involves an understanding of object oriented programming, because that it how the Joomla coders set up the code structure. No big deal if you already have done OO in languages like Java or C++. Whereas any earlier programming in a PHP file might typically have meant that you could ignore OO concepts. While PHP certainly allows OO, the smaller scale effort where you focus on one or 2 PHP files, and the often short lengths of those files meant that you could often have ignored any explicit OO issues.
This book is a wide treatise on how to customize VirtueMart layout, based on the "theme" which is a concept introduced in VirtueMart since version 1.1.0. It is perfect for everyone who needs to customize VirtueMart by hacking the code. The reader should have already a good knowledge of VirtueMart and a little skill in HTML / PHP.
Joseph explains us: * what is a theme * how it works * which files and folders are contained in a theme * and most of all, how we can adapt a theme for our needs
Now, this book has one main defect in my opinion: it is very long. * in the first part of the book, there are explanations which goes slightly OT * the writing style is not really concise * there is very limited amount of diagrams, images, tables and other formats of visual reporting which could have made the book easier to read
That said, the author knows his stuff. As a fellow VirtueMart developer I was able to appreciate his overall knowledge of the software.