O'Reilly's XML IN A NUTSHELL is, like all entries in the Nutshell series, a desktop quick reference. It provides concise information about nearly all matters of XML, and is split into roughly four parts. The first introduces XML, the concept of tags, well-formedness, Unicode, DTD's and schemas, namespaces, and so forth. The second provides an overview for the many formats that are built upon XML, such as XHTML, XSL:FO, Docbook, etc., and technologies that plug-in into XML, namely XSLT, XPath, XLinks, XPointers, XInclude, and CSS. The fourth covers DOM and SAX, the APIs for dealing with XML. Finally, the book ends with a "Reference section" for various technologies covered earlier in the book, structured much like O'Reilly's pocket guides. I found the Reference section somewhat inconvenient, it causes flipping back and forth when each section could have been simply integrated with the previous discussion of the relevant technology earlier in the book. Furthermore, the book ends with a long series of Unicode character tables, which are of limited utility, as they cover only a portion of Unicode, which has already expanded in the time since, and these tables simply bloat the book a little.
This third edition is especially admirable for its advocation of schemas, whereas many other XHTML publications would mention only DTDs.
XML IN A NUTSHELL is emphatically not a tutorial for XML, in spite of the friendly introduction to the markup language that opens the book. For each of the technologies mentioned herein, you'll want a separate book. For XPath especially, O'Reilly's XPATH AND XPOINTER is worth getting. XML IN A NUTSHELL instead provides only a quick reference for matters the reader is already acquainted with. Now, much of this quick reference information can be freely had on the Web. I'd recommend the book only to those who are fortunate enough to have someone else cover their book expenses, or can get it from their library, or those who simply adore print documentation.