<?php

$xml = simplexml_load_string('<entry>
 <cap:stuff>
  <valueName>aaa</valueName>
  <value>000</value>
  <valueName>bbb</valueName>
  <value>111</value>
 </cap:stuff>
</entry>');

echo "\nResult:", $xml->stuff->value[1], "\n\n";
echo "XML:\n", $xml->asXML();

Warning: simplexml_load_string(): namespace error : Namespace prefix cap on stuff is not defined on line 10

Warning: simplexml_load_string():  <cap:stuff> on line 10

Warning: simplexml_load_string():            ^ on line 10

Result:111

XML:
<?xml version="1.0"?>
<entry>
 <stuff>
  <valueName>aaa</valueName>
  <value>000</value>
  <valueName>bbb</valueName>
  <value>111</value>
 </stuff>
</entry>