public function validation($data, $files) {
        $errors = parent::validation($data, $files);

        if (!array_key_exists('setting_root_filename', $errors)) {
            if (trim($data['setting_root_filename']) == '') {
                $errors['setting_root_filename'] = get_string('errorfilenamerequired', 'backup');
            } else if (strlen(trim($data['setting_root_filename'])) > 255) {
                $errors['setting_root_filename'] = get_string('errorfilenametoolong', 'backup');
            } else if (!preg_match('#\.mbz$#i', $data['setting_root_filename'])) {
                $errors['setting_root_filename'] = get_string('errorfilenamemustbezip', 'backup');
            }
        }

        return $errors;
    }