$dom = new DOMDocument();
$element = $dom->createElement("div");
$element->setAttribute("id", "id1");
$dom->appendChild($element);
$tmp = $dom->createDocumentFragment();
$tmp->appendXML('<h1>Hello <b>World!</b></h1>');
$xpath = new DOMXPath($dom);
$xpath->query("//*[@id='id1']")->item(0)->appendChild($tmp);
echo $dom->saveHTML();
ideone.com/KnSQ8l curl_setopt($ch, CURLOPT_HEADERFUNCTION, array('ClassName', 'CallbackMethod'));
и/илиcurl_setopt($ch, CURLOPT_HEADERFUNCTION, 'ClassName::CallbackMethod');