如何使用DOMDocument将子元素添加到head标记

Question

我正在尝试通过收集分发的<style>标记并将其全部删除然后将新的标记添加到head来安排文档，我已编写此代码段，但遗漏了如何添加新的style标记到标题

    ob_start('ob_postprocess');
// ob_postprocess is our custom post processing function
function ob_postprocess($buffer){
    $d = new DOMDocument('1.0','UTF-8');
    $d->loadHTML($buffer);

    $x = new DOMXPath($d);
    $t = $x->evaluate("//text()");
    $cc = array();
    foreach($d->getElementsByTagName('style') as $style){
            $cc[]= $style->nodeValue;
            $style->parentNode->removeChild($style);
    }
    foreach($d->getElementsByTagName('head') as $head){
        //add new style tag
    }
    $buffer = $d->saveHTML($d);
    return $buffer;
}