public function config_form_definition(\MoodleQuickForm $mform) {
        $mform->addElement('header', 'course_handler_header', get_string('customfieldsettings', 'core_course'));
        $mform->setExpanded('course_handler_header', true);

        // If field is locked.
        $mform->addElement('selectyesno', 'configdata[locked]', get_string('customfield_islocked', 'core_course'));
        $mform->addHelpButton('configdata[locked]', 'customfield_islocked', 'core_course');

        // Field data visibility.
        $visibilityoptions = [self::VISIBLETOALL => get_string('customfield_visibletoall', 'core_course'),
            self::VISIBLETOTEACHERS => get_string('customfield_visibletoteachers', 'core_course'),
            self::NOTVISIBLE => get_string('customfield_notvisible', 'core_course')];
        $mform->addElement('select', 'configdata[visibility]', get_string('customfield_visibility', 'core_course'),
            $visibilityoptions);
        $mform->addHelpButton('configdata[visibility]', 'customfield_visibility', 'core_course');
    }