This huge book is both a beginners guide to using ZSLT and a complete reference book.
If the second half of this book were all that the book contained then it would belong in O'Reilly's Definitive Guide series and would be one of the better books in that series. The addition of the chapetrs in the front of the book make this much more than that.
With this book on your bookshelf you will know exactly where to go whenever you have a problem that is related to XSLT. By studying the first few chapters someone who knows what XSLT is but has never used it before will learn enough to get them started. After that the complete reference that makes up the latter part of the book will provide answers to whatever issues you have subsequently.
Regardless of your current knowledge of XSLT, this book will be the only one that you will ever need (at least until another version of XSLT comes out).