<?php
$address = array(
    'name' => 'Burgstaller',
    'firstname' => 'Boris',
    'address' => array(
        'street' => 'No idea',
   ),
);

$dom = new DOMDocument();
$dom->loadXML('<address/>');
api_helpers_xml:: array2dom($address, $dom, $dom->documentElement);

echo $dom->saveXML();