php xpath 采集数据

$oldSetting = libxml_use_internal_errors(true);
libxml_clear_errors();

$dom = new DOMDocument();
$dom->loadHTMLFile('http://91baby.mama.cn/forum.php?mod=viewthread&tid=1080068&extra=&authorid=9212619&page=1');
$xml = simplexml_import_dom($dom);

$getContents = $xml->xpath('//*[@id="postmessage_22195681"]/font');

print_r($getContents); exit;