A use exemple of this method :
Usefull for generating an XML linked with a XSLT !
<?php
$xml = new DOMDocument( "1.0", "ISO-8859-15" );
$xml->preserveWhiteSpace = false;
$xml->formatOutput = true;
$xslt = $xml->createProcessingInstruction('xml-stylesheet', 'type="text/xsl" href="base.xsl"');
$xml->appendChild($xslt);
$root = $xml->createElement("list");
$node = $xml->createElement("contact", "John Doe");
$root-> appendChild($node);
$xml-> appendChild($root);
$xml-> save("output.xml");
?>
output.xml :
<?xml version="1.0" encoding="ISO-8859-15"?>
<?xml-stylesheet type="text/xsl" href="base.xsl"?> //the line has been created successfully
<list>
<contact>John Doe</contact>
</list>