Use DomDocument how to get innerHTML of element

Function:
function innerHTML($element) {
    $pObject = new DOMDocument( '1.0', 'utf-8');
    $pObject->appendChild( $pObject->importNode( $element, true ));
    return $pObject->saveHTML();
}

Example:
$dom = new DomDocument('1.0', 'utf-8');
$dom->loadHTML($content);
$divs = $dom->getElementsByTagName('div');
$ndiv = $divs->length;
for ($i = 0; $i < $ndiv; $i++) {
    $div = $divs->item($i);
    if ($div->hasAttributes()) {
        $attributes = $div->attributes;
        foreach ($attributes as $j => $attribute) {
            if ($attribue->name == 'class' && $attribute->value=='you-are-looking-for') {
                $innerHTML = innerHTML($div);
            }
        }
    }
}