/**
  * Constructor. Also generates a boundary of the form
  * <pre>
  * ----=_Alternative_10424693873e22d20b43b490.00112051
  * </pre>
  *
  * @param   peer.mail.MimePart* parts
  */
 public function __construct()
 {
     parent::__construct();
     $this->charset = '';
     for ($i = 0, $s = func_num_args(); $i < $s; $i++) {
         $this->addPart(func_get_arg($i));
     }
     $this->setBoundary('----=_Alternative_' . uniqid(time(), TRUE));
 }