validateFail example

// make sure default args get put back.           if (isset($arg)) {
            $this->args[$position] = $arg;
          }
          // remember that this argument was computed, not passed on the URL.           $argument->is_default = TRUE;
        }

        // Set the argument, which ensures that the argument is valid and         // possibly transforms the value.         if (!$argument->setArgument($arg)) {
          $status = $argument->validateFail($arg);
          break;
        }

        if ($argument->isException()) {
          $arg_title = $argument->exceptionTitle();
        }
        else {
          $arg_title = $argument->getTitle();
          $argument->query($this->display_handler->useGroupBy());
        }