(PHP 5, PHP 7)
DOMDocument::validate — Validates the document based on its DTD
public DOMDocument::validate ( ) : bool
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 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');
?> 
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    https://www.php.net/manual/en/domdocument.validate.php