I received this book through a Humble Bundle and had to brush up on my ancient XML skills, so I thought a book that was "revised in 2020" would help me do that. I was utterly disappointed. The book refers to Internet Explorer 4.0 and IE5 as current technologies. SOAP has not been called "Simple Object Access Protocol" since the release of version 1.2 in 2007. Sibling elements in XML are not called "brothers" nor "sisters." CSS2 is described as a work in progress having limited support in web browsers, with no mention of CSS Level 3. The author correctly writes that XML elements are case-sensitive, but then the examples show inconsistent case everywhere without mentioning that this creates invalid XML. The biggest issue I have with this book is that about half of the content seems to be plagiarized from other sources without giving any credit to the original authors. Appendix A has been copied from an old RealProducer manual, and Appendix C is an old XML tutorial from php.net. None of those sources exist in today's world anymore, but by including incomplete copy pasta the author created continuity issues within the flow of the book. Often, I see "As we saw in the previous chapter, ...", but what the text refers to was never described in the previous chapter. I feel I have wasted 40 hours of my life going through this drivel without learning anything new about XML.