(PHP 5, PHP 7, PHP 8)
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.
  
This function has no parameters.
   Returns true on success or false on failure.
   If the document has 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');
?>