I have an extremely simple implementation that pulls in a test bit of XML and attempts to validate it using DOMDocument. In testing, it's able to get through the LoadHTML() call fine, but as soon as I try and run validate(), the browser hangs forever and doesn't load. Here's the code:
$content = '<?xml version="1.0" encoding="utf-8"?><mainElement></mainElement>';
$dom = new DOMDocument;
$dom->LoadHTML($content);
if (!$dom->validate()) {
echo 'fail';
} else {
echo 'success!';
}
It seems that if you want to validate content loaded with loadHTML, you need DOCTYPE declaration (without it, you get an infinitive loop). For example, following code works and prints fail
$content = "
<!DOCTYPE html>
<html>
<body>
Content of the document......
</body>
</html>
";
$dom = new DOMDocument();
$dom->loadHTML($content);
if (!$dom->validate()) {
echo 'fail';
} else {
echo 'success!';
}
For XML it's more tolerant (it works even you didn't declare dtd but it returns false). In your case, you might use loadXML method and your code will print fail.
Tested with php 7.0.13.