Today I ran into a small problem, validating import XML data against a DTD(Document Type Definition), and discovered a neat way to solve this without PHP4's own means, as the PHP 4 version on the running system wasn't supporting the DOM XML Functions. Xmllint, a command line XML tool, parses provided XML files and can be used to verify that these files are well formed and are satisfying an associated DTD/XML Schema.

In his example he shows a simple implementation of the tool, grabbing the file's information and pushing it through a command line request to check the file.