What is the relationship between site.xml and book.xml?
One site.xml file in your project root can replace all the book.xml files (one per directory) in your site. Internally, Forrest uses site.xml to dynamically generate book.xml files. However, Forrest first checks for the existence of a book.xml file, so backwards-compatibility is preserved. If a directory has a book.xml file, the book.xml will be used to generate the menu. This supplement is useful in situations where site.xml-generated menus aren’t appropriate. See Menus and Linking.
