<?php
$dom = new DOMDocument('1.0', 'iso-8859-1');
$element = $dom->appendChild(new DOMElement('root'));
$element_ns = new DOMElement('pr:node1', 'thisvalue', 'http://xyz');
$element->appendChild($element_ns);
echo $dom->saveXML(); /* <?xml version="1.0" encoding="iso-8859-1"?>
<root><pr:node1 xmlns:pr="http://xyz">thisvalue</pr:node1></root> */
?>