The first 1/3 defines DTD syntax. This section is horrible unless you already know it. It briefly mentions a topic and regurgitates a definition and then fails to explain the syntax and intricasies. The 2nd 1/3 covers some examples. However, this is done at a very high level. It explains almost nothing about how they work. The last 1/3 is worthwhile and covers some interesting advanced topics. This book is only worth something to someone who is not interested in hands-on XML development. Also, it was confusing how it kept describing SGML-only features and mixing these with the SGML/XML features.