protected function add_default_hidden_elements($mform) {
        global $USER;

        // Add some hidden fields.
        $mform->addElement('hidden', 'id');
        $mform->setType('id', PARAM_INT);
        $mform->setDefault('id', 0);

        $mform->addElement('hidden', 'userid');
        $mform->setType('userid', PARAM_INT);
        $mform->setDefault('userid', $USER->id);

        $mform->addElement('hidden', 'modulename');
        $mform->setType('modulename', PARAM_INT);
        $mform->setDefault('modulename', '');

        $mform->addElement('hidden', 'instance');
        $mform->setType('instance', PARAM_INT);
        $mform->setDefault('instance', 0);

        $mform->addElement('hidden', 'visible');
        $mform->setType('visible', PARAM_INT);
        $mform->setDefault('visible', 1);
    }