This series has so far focused on XML technologies and how they can be utilised using PHP 5. A subject we have not touched upon yet, is XML validation. This article will explore the application independent XML validation standards of DTD's, the XML Schema Language and the XSLT-based Schematron language.

They point back to part one of the series for the XML library they'll use and waste no time getting right into the code. They demonstrate a simple validation first before moving on to the use of DTDs to ensure the correct content. Next up is more work with the XML schemas continuing on to the Schematron functionality (their use and validation).