This book appears to have been thrown together overnight, without the attention of a proofreader or content editor. While I can't say it's actually missing important content, it is certainly the sloppiest O'Reilly book I've ever read. The very first example (on p. 6) is a glaringly ill-formed XML document (the second line contains spurious junk text, as if from a word-processing error), and it just continues from there. The book contains numerous apparent "cut-and-paste" errors of this kind, as well as evidence that global search-and-replace operations were hastily performed on the entire text without subsequent proofreading. What's up, O'Reilly?