<?php
$dom = new DOMDocument('1.0', 'utf-8');
$element = $dom->appendChild(new DOMElement('root'));
$attr = $element->setAttributeNode(new DOMAttr('attr', 'attrvalue'));
echo $dom->saveXML();
?>
The above example will output:
<?xml version="1.0" encoding="utf-8"?>
<root attr="attrvalue"/>