Appendix E. Reading a Document Type Definition

This appendix presents the Document Type Definitions (DTDs) for HTML 4.01 and XHTML 1.0. Traditional HTML “dialects” are defined using SGML (Standard Generalized Markup Language), a complex language with many nuances. XHTML dialects are developed in XML (Extensible Markup Language), which is a subset of SGML and slightly easier to work with. This appendix presents the small amount of SGML or XML knowledge needed to read the various DTDs found online directly.