- var_dump: documentation ( source)
<?php
$html = <<<HTML
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title></title>
</head>
<body>
<script type="text/javascript">
var content = '<!DOCTYPE html><html><head></head><body></body></html>'
</script>
<div id="test">test</div>
</body>
</html>
HTML;
$dom = new DOMDocument('1.0', 'UTF-8');
$dom->validateOnParse = true;
$dom->loadHTML($html);
$xpath = new \DOMXPath($dom);
var_dump($xpath->query("descendant-or-self::*[@id = 'test']", $dom));
?>