DTD: Document Type Definition [L1 ]
Adjunct to XML and SGML. markup declarations that provide a grammar for a class of documents. Defines how tags can be nested, follow each other, etc. Essentially describes the contents of each valid tags as a regular expression. Beyond that it defines the attributes per tag, and their type.
Simple example:
<!ELEMENT database (record+) > <!ELEMENT record (firstname,lastname,phone+)> <!ATTLIST record created NMTOKEN #IMPLIED > <!ELEMENT firstname (PCDATA)> <!ELEMENT lastname (PCDATA)> <!ELEMENT phone (PCDATA)>
tDom with its extension tnc can validate XML documents by a given DTD. LV 2007 Oct 09 - it isn't clear how tdom can validate xml documents by a given DTD.
As the language of DTDs differs from XML, it is considered old-fashioned, and several replacements (which follow XML syntax) have been proposed: XML Schema, ...
MAKR: There is fun project called A little XML Schema validator ...