protected function view_plugin_grading_batch_operation($mform) {
        require_capability('mod/assign:grade', $this->context);
        $prefix = 'plugingradingbatchoperation_';

        if ($data = $mform->get_data()) {
            $tail = substr($data->operation, strlen($prefix));
            list($plugintype, $action) = explode('_', $tail, 2);

            $plugin = $this->get_feedback_plugin_by_type($plugintype);
            if ($plugin) {
                $users = $data->selectedusers;
                $userlist = explode(',', $users);
                echo $plugin->grading_batch_operation($action, $userlist);
                return;
            }
        }
        print_error('invalidformdata', '');
    }