(PHP 5, PHP 7)
SimpleXMLElement::xpath — Runs XPath query on XML data
$path
   ) : array
   The xpath method searches the SimpleXML node for
   children matching the XPath path.
  
pathAn XPath path
   Returns an array of SimpleXMLElement objects or FALSE in
   case of an error.
  
Example #1 Xpath
<?php
$string = <<<XML
<a>
 <b>
  <c>text</c>
  <c>stuff</c>
 </b>
 <d>
  <c>code</c>
 </d>
</a>
XML;
$xml = new SimpleXMLElement($string);
/* Search for <a><b><c> */
$result = $xml->xpath('/a/b/c');
while(list( , $node) = each($result)) {
    echo '/a/b/c: ',$node,"\n";
}
/* Relative paths also work... */
$result = $xml->xpath('b/c');
while(list( , $node) = each($result)) {
    echo 'b/c: ',$node,"\n";
}
?>
The above example will output:
/a/b/c: text /a/b/c: stuff b/c: text b/c: stuff
Notice that the two results are equal.