[Rimer dal]

This is untested but it is the concept... I think it is was what you wanted.

<?php

function add_data($StringToAdd){
$filename = 'test.txt';

// Let's make sure the file exists and is writable first.
if (is_writable($filename)) {

   if (!$handle = fopen($filename, 'r+')) {
         echo "Cannot open file ($filename)";
         exit;
   }
   
   $contents = fread($handle, filesize($filename));
   if(stripos("<item>")){
      $chunk1 = substr($contents,0,stripos("<item>"));
      $chunk2 = substr($contents,stripos("<item>"));
      $contents = $chunk1.$StringToAdd.$chunk2;
   }else{
       echo "Did not find <item>";
       exit;
   }

   if (fwrite($handle, $contents) === FALSE) {
       echo "Cannot write to file ($filename)";
       exit;
   }
   
   echo "Success, wrote ($contents) to file ($filename)";
   
   fclose($handle);

} else {
   echo "The file $filename is not writable";
}
?>