Question

Is there a way (without installing any libraries) of validating XML using a custom DTD in PHP?

Answer 1

Take a look at PHP’s DOM, especially DOMDocument::schemaValidate and DOMDocument::validate.

The example for DOMDocument::validate is fairly simple:

<?php $dom = new DOMDocument; $dom->Load('book.xml'); if ($dom->validate()) {     echo "This document is valid!\n"; } ?>