php domdocument unwrap first div

$dom = new DOMDocument();

$dom->loadHTML(
'<div class="page">
    <div class="wrapper">
        <div class="content">
            <p>Hello World!</p>
        </div>
    </div>
</div>');

$divs = $dom->getElementsByTagName('div');

$wrapper = $divs->item(0);

while($wrapper->firstChild) {
    $wrapper->parentNode->insertBefore($wrapper->firstChild, $wrapper);
}

$wrapper->parentNode->removeChild($wrapper);

echo $dom->saveHTML();