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<?php

$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();
Success #stdin #stdout 0.03s 52480KB
stdin
Standard input is empty
stdout
<div id="id1"><h1>Hello <b>World!</b></h1></div>