<?php
/* Load the two XML sources */
$xml = new DomDocument; // from /ext/dom
$xml->load('simpletree.xml');

$xsl = new DomDocument;
$xsl->load('simpletree.xsl');

/* Configure the transformer */
$proc = new xsltprocessor;
$proc->importStyleSheet($xsl); // attach the xsl rules
/* the function below will write an file contain all infos about the two files above */
$proc->transformToURI($xml, 'file.txt');
?>

$xml = new DomDocument;

$xml->load('simpletree.xml');

$xsl->load('simpletree.xsl');

$proc = new xsltprocessor;

$proc->transformToURI($xml, 'file.txt');