PhP通过id获取元素不起作用

Question

I'm trying to do a php file using DOM in order to append a few table rows to my table whenever my SQL table is updated. The problem is, the function getElementById never works and i don't get why. here's the code:

$doc = new DomDocument();
$doc->validateOnParse = true; 
$doc->load('home.php');
$element = $doc->getElementById('table-responsive');   //this is a div
$teste = $doc->createElement('div');
$element->appendChild($test);

I always get error 500 because the getElementById is not found/ doesn't work. Any ideas ?