A document type definition (DTD) is a set of declarations that conform to a particular markup syntax. It describes a class, or type, of SGML or XML documents. With a DTD, XML documents can be validated. This is useful if you want to check the allowed structure for a certain XML instance.

Profiling describes a filtering mechanism. An XML document can hold different versions in one file, like different architectures, platforms, operating systems, or user levels. The author inserts profiling information into XML documents at specific places and the profiling mechanism selects only those parts that are relevant. This solves the problem of having lots of files with only minor differences. The author has to maintain only one file, but has to take care of the correct profiling information.

Profiling information is inserted with the attributes os and arch.

Project profiles contain information needed to select the correct profiling information. The first step to build a book is to source the project profile in your current shell. This sets all the relevant variables needed by our Makefiles.

See Also profiling.

Valid means that an XML document is well-formed and adheres to a certain DTD.

See Also DTD (Document Type Definition), well-formed.

An XML document is well-formed if a start tag and an end tag have the same name, each tag contains only valid characters according to the XML specification, the nesting is correct (every start tag must have a corresponding end tag), and attribute values are enclosed by single (') or double quotes (").

XSL-FO (or just FO) is a specification for describing page layouts. The book production process needs it as an intermediary file for building PDFs.