perché non riesco a scrivere su file XML?

[wormhole]

Reinvio nuovamente il mio codice in maniera più umana.

Ecco il mio codice:

<?php
     $dom  = new DomDocument();
     $dom->load("articles.xml");      // writing to the DOM
     $item = $dom->createElement("item");
     $title = $dom->createElement("title");
     $titletext = $dom->createTextNode("XML in PHP5");
     $title->appendChild($titletext);
     $item->appendChild($title);
     $dom->documentElement->appendChild($item);
    print $dom->saveXML();  ?>

Ed il file XML:

<?xml version="1.0" encoding="iso-8859-1" ?>
 <articles>
     <item>
           <title>PHP Weekly: Issue # 172</title>
           <link>[url]http://www.zend.com/zend/week/week172.php[/url]</link>
       </item>
     <item> 
          <title>Tutorial: Develop rock-solid code in PHP: Part three</title>
           <link>[url]http://www.zend.com/zend/tut/tut-hatwar3.php[/url]</link>
       </item>
 </articles>

gp