public function definition() {
        $mform = $this->_form;

        $this->definition_inner($mform);

        $mform->addElement('hidden', 'contextid');
        $mform->setType('contextid', PARAM_INT);
        $mform->setDefault('contextid', $this->context->id);

        $mform->addElement('hidden', 'filter');
        $mform->setType('filter', PARAM_SAFEPATH);
        $mform->setDefault('filter', $this->filter);

        $this->add_action_buttons();
    }