This book is written in the DocBook/XML markup language. You may find the following web pages useful if you want to hack DocBook:
Norman Walsh's DocBook page . This is the basic DocBook resource page. Norman Walsh is heavily involved in the DocBook standardization process and he is the author of the main tools for processing DocBook markup and converting it to HTML or other formats.
DocBook: The Definitive Guide . An O'Reilly book, also available online, with a complete reference of the DocBook markup language.
GNOME Documentation Project . The main author of this book is heavily involved in the GNOME Project, which uses DocBook for its documentation system. The GNOME Documentation Project page contains a lot of useful information about writing documents and user manuals.