<?php
$xml=<<<XML
<book xmlns:chap="http://example.org/chapter-title">
&nbsp;&nbsp;  <title>My Book</title>
&nbsp;&nbsp;  <chapter id="1">
&nbsp;&nbsp;&nbsp;&nbsp;    <chap:title>Chapter 1</chap:title>
&nbsp;&nbsp;&nbsp;&nbsp;    <para>Donec velit. Nullam eget tellus...</para>
&nbsp;&nbsp;  </chapter>
&nbsp;&nbsp;  <chapter id="2">
&nbsp;&nbsp;&nbsp;&nbsp;    <chap:title>Chapter 2</chap:title>
&nbsp;&nbsp;&nbsp;&nbsp;    <para>Lorem ipsum dolor sit amet....</para>
&nbsp;&nbsp;  </chapter>
</book>
XML;

$sxe=new SimpleXMLElement($xml);
$sxe->registerXPathNamespace('c', 'http://example.org/chapter-title');
$result=$sxe->xpath('//c:title');
foreach ($result as $title)
&nbsp;&nbsp;  {
&nbsp;&nbsp;  echo $title . "<br>";
&nbsp;&nbsp;  }
?>