This book is organized as an advanced tutorial that can also serve as a solid and comprehensive reference. Chapter 1 covers the bare minimum material needed to start working with XML, although for the most part this is not intended as a comprehensive introduction, but more as a review for readers who already have read other, more basic books. Chapter 2 introduces RSS, XML-RPC, and SOAP, the XML applications used for examples throughout the rest of the book. This is followed by two chapters on generating XML from your own programs (a subject all too often presented as a lot more complicated than it actually is). Chapter 3 covers generating XML directly from code, and Chapter 4 covers converting legacy data in other formats to XML. The remaining bulk of the book is devoted to the major APIs for processing XML:
Finally, the book finishes with an appendix providing quick references to the main APIs.
If you have limited experience with XML, I suggest that you read at least the first five chapters in order. From that point forward, if you have a particular API preference, you may begin with the part that covers the major API you're interested in:
Once you're comfortable with one or more of these APIs, you can read Chapters 16 and 17 on XPath and XSLT. However, those APIs and chapters do require some knowledge of at least one of the three major APIs.