(PHP 5, PHP 7)
DOMDocument::validate — Validates the document based on its DTD
Validates the document based on its DTD.
You can also use the validateOnParse property of DOMDocument to make a DTD validation.
   Returns TRUE on success or FALSE on failure.
   If the document have no DTD attached, this method will return FALSE.
  
Example #1 Example of DTD validation
<?php
$dom = new DOMDocument;
$dom->Load('book.xml');
if ($dom->validate()) {
    echo "This document is valid!\n";
}
?>
You can also validate your XML file while loading it:
<?php
$dom = new DOMDocument;
$dom->validateOnParse = true;
$dom->Load('book.xml');
?>