/**
  * Dumps the internal XML tree back into a file with added whitespace 
  * (new-lines and tabbing).
  * 
  * @param string $source
  * @param optional int $options
  * @return void
  * @access public
  * @since 1/23/08
  */
 public function saveWithWhitespace($filename, $options = null)
 {
     $doc = new Harmoni_DOMDocument();
     if ($this->documentElement) {
         $doc->appendChild($doc->importNode($this->documentElement, true));
     }
     $doc->addWhitespaceToDocument();
     $doc->save($filename, $options);
 }