Book excerpt: What is this book about? XPath 2.0 Programmer's Reference is the only authoritative reference on XPath, a sub-language within XSLT that determines which part of an XML document the XSLT transforms. Written for professional programmers who use XML every day but find the W3C XPath specifications tough to slog through, this book explains in everyday language what every construct in the language does and how to use it. It also offers background material on the design thinking behind the language, gentle criticism of the language specification when appropriate, and a diverse range of interesting examples in various application areas.