Xform xml parsing

PHP
1

In my PHP application i’m using xforms and i need to parse the xml and i would like to access the id of node from xml. I tried normal xml for access id of node and its work fine. But when i tried that approach in xfrom xml, i cant access the id of node. This is the code i tried. In this i need the id of node test_geopoint. Here the node name will changed for each xml forms, so i prefered to access the id of node next to <instance>. How can access the id of that node?
thanks.

<?php
$xmlstr = <<<XML
<?xml version="1.0"?>
<h:html xmlns="http://www.w3.org/2002/xforms" xmlns:ev="http://www.w3.org/2001/xml-events" xmlns:h="http://www.w3.org/1999/xhtml" xmlns:jr="http://openrosa.org/javarosa" xmlns:orx="http://openrosa.org/xforms/" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <h:head>

    <model>
      <instance>
        <test_geopoint id="test_geopoint">
          <name/>
          <geopoint/>
          <meta>
            <instanceID/>
          </meta>
        </test_geopoint>
      </instance>
      <bind nodeset="/test_geopoint/name" type="string"/>
      <bind nodeset="/test_geopoint/geopoint" type="geopoint"/>
      <bind calculate="concat('uuid:', uuid())" nodeset="/test_geopoint/meta/instanceID" readonly="true()" type="string"/>
    </model>
  </h:head>
  <h:body>
    <input ref="/test_geopoint/name">
      <label>What is the name of this store?</label>
    </input>
    <input ref="/test_geopoint/geopoint">
      <label>Collect the GPS coordinates of this store.</label>
      <hint>GPS coordinates can only be collected when outside.</hint>
    </input>
  </h:body>
</h:html>

XML;

$movies = new SimpleXMLElement($xmlstr);


//echo $movies->idList->ids['id'];
echo $movies->model->instance->children()[0]['id'];
?>