6.3 Further reading

The W3C XML 1.0 Specification: http://www.w3.org/TR/2006/REC-xml-20060816/
The formal and official definition of XML. Quite technical.
The w3schools XML Tutorial: http://www.w3schools.com/xml/
Quick, basic tutorial-based introduction to XML.
The w3schools DTD Tutorial: http://www.w3schools.com/dtd/
Quick, basic tutorial-based introduction to DTDs.
The W3C Validation Service: http://validator.w3.org/
This will check raw XML files as well as HTML documents.
libxml2: http://xmlsoft.org/
This software includes a command-line tool, xmllint for checking XML code, including validating it against a DTD.

Paul Murrell