There are also a number of books worth checking out:
Developing SGML
DTDs: From Text to
Model to Markup, Eve Maler
and Jeanne El Andaloussi,
0-13-309881-8, Prentice-Hall PTR, Upper Saddle River, 1996.
Practical SGML,
Erik van Herwijnen, 2, 0-7923-9434-8,
Kluwer Academic Press, 1994.
The SGML Handbook,
Charles Goldfarb and Yuri Rubinksy, 0-7923-9434-8, 1991, Oxford
University Press.
SGML: an author's guide to the Standard Generalized Markup
Language, Martin Bryan,
0-201-17535-5, 1988, Addison-Wesley Publishing Company.
$GML: The Billion Dollar Secret, Chet Ensign, 0-13-226705-5, 1998, Prentice
Hall.
Creating Documents with XML, Chris
Maden, 1-56592-518-1, 1999, O'Reilly & Associates.
XML: A Primer,
Simon St. Laurent, 1-5582-8592-X, 1998,
MIS:Press/IDG Books Worldwide.
Understanding SGML and XML Tools, Peter Flynn, 0-7923-8169-6, 1998, Kluwer Academic
Publishers.
The LaTeX Web Companion: Integrating TeX, HTML,
and XML, Michel Goosens
and Sebastian Rahtz, 0-201-43311-7,
1999, Addison-Wesley Publishing Company.