W3School tutorial: The best place to start. XML Guide - very detailed tutorial, each and every DTD's aspect is described and illustrated with examples. ZVON's DTD tutorial � a lot of examples too. And finally, if you are going to write real-world DTDs, this is highly thought provoking text: Structuring XML Documents, by David Megginson CHAPTER 3: Ease of Learning.
[This message has been edited by Mapraputa Is (edited March 19, 2001).]