(PHP 5, PHP 7)
DOMDocument::xinclude — Substitutes XIncludes in a DOMDocument Object
$options
  ] )This method substitutes » XIncludes in a DOMDocument object.
Note:
Due to libxml2 automatically resolving entities, this method will produce unexpected results if the included XML file have an attached DTD.
   Returns the number of XIncludes in the document, -1 if some processing failed,
   or FALSE if there were no substitutions.
  
Example #1 DOMDocument::xinclude() example
<?php
$xml = <<<EOD
<?xml version="1.0" ?>
<chapter xmlns:xi="http://www.w3.org/2001/XInclude">
 <title>Books of the other guy..</title>
 <para>
  <xi:include href="book.xml">
   <xi:fallback>
    <error>xinclude: book.xml not found</error>
   </xi:fallback>
  </xi:include>
 </para>
</chapter>
EOD;
$dom = new DOMDocument;
// let's have a nice output
$dom->preserveWhiteSpace = false;
$dom->formatOutput = true;
// load the XML string defined above
$dom->loadXML($xml);
// substitute xincludes
$dom->xinclude();
echo $dom->saveXML();
?>
The above example will output something similar to:
<?xml version="1.0"?>
<chapter xmlns:xi="http://www.w3.org/2001/XInclude">
  <title>Books of the other guy..</title>
  <para>
    <row xml:base="/home/didou/book.xml">
       <entry>The Grapes of Wrath</entry>
       <entry>John Steinbeck</entry>
       <entry>en</entry>
       <entry>0140186409</entry>
      </row>
    <row xml:base="/home/didou/book.xml">
       <entry>The Pearl</entry>
       <entry>John Steinbeck</entry>
       <entry>en</entry>
       <entry>014017737X</entry>
      </row>
    <row xml:base="/home/didou/book.xml">
       <entry>Samarcande</entry>
       <entry>Amine Maalouf</entry>
       <entry>fr</entry>
       <entry>2253051209</entry>
      </row>
  </para>
</chapter>