Remove all namespaces from XML in PHP (dirty hack)

remove-namespaces-xml.php

<?php

$dom = new DOMDocument();
$dom->preserveWhiteSpace = false;
$dom->formatOutput = true;
$dom->loadXML(file_get_contents(__DIR__ . '/demo.xml'));

$dom = removeAllNamespaces($dom);

$dom->save('demo-out.xml');

function removeAllNamespaces(DOMDocument $domSource): DOMDocument
{
    $dom = new DOMDocument();
    $dom->formatOutput = true;
    
    $domSource = clone $domSource;
    $domSource->formatOutput = true;

    $dom->loadXML(preg_replace('/\sxmlns="(.*?)"/', '', $domSource->saveXML()));
    $xpath = new DOMXPath($dom);

    /** @var \DOMNameSpaceNode|DOMAttr $namespaceNode */
    foreach ($xpath->query('//namespace::*') as $namespaceNode) {
        $prefix = str_replace('xmlns:', '', $namespaceNode->nodeName);
        $nodes = $xpath->query("//*[namespace::{$prefix}]");

        /** @var DOMElement $node */
        foreach ($nodes as $node) {
            $namespaceUri = $node->lookupNamespaceURI($prefix);
            $node->removeAttributeNS($namespaceUri, $prefix);
        }
    }

    // Important: Reload document to remove invalid xpath references from old dom
    $dom->loadXML($dom->saveXML());

    return $dom;
}