This book was helpful while learning XPath 2.0, but I recommend reading the 4th edition instead. XPath 2.0 was still in draft form when this book was published. The 4th edition covers the official XPath 2.0 spec and has numerous corrections. The XSLT 2.0 and XPath 2.0 books were also merged into a single book in the 4th edition. And the organization/writing is much better.