public function backup_details_unknown(moodle_url $nextstageurl) {

        $html  = html_writer::start_div('unknownformat');
        $html .= $this->output->heading(get_string('errorinvalidformat', 'backup'), 2);
        $html .= $this->output->notification(get_string('errorinvalidformatinfo', 'backup'), 'notifyproblem');
        $html .= $this->output->single_button($nextstageurl, get_string('continue'), 'post');
        $html .= html_writer::end_div();

        return $html;
    }