/**
  * This function sets the output ressource. The following elements are possible.
  * <ul>
  *   <li>SCREEN</li>
  * </ul>
  *
  * @param String output The resource to output.
  */
 public static function setOutput($out)
 {
     if (!InputValidator::isOutputRessource($out)) {
         return;
     }
     self::$OUT = $out;
 }