protected function getHtmlFrag($html)
    {
        if (!($html = (string) $html)) {
            return []; // Nothing to do.
        }
        if (preg_match('/(?P<all>(?P<open_tag>\<html(?:\s+[^>]*?)?\>)(?P<contents>.*?)(?P<closing_tag>\<\/html\>))/uis', $html, $html_frag)) {
            return $this->removeNumericKeysDeep($html_frag);
        }
        return [];
    }