public function navigation_panel(quiz_nav_panel_base $panel) {

        $output = '';
        $userpicture = $panel->user_picture();
        if ($userpicture) {
            $fullname = fullname($userpicture->user);
            if ($userpicture->size === true) {
                $fullname = html_writer::div($fullname);
            }
            $output .= html_writer::tag('div', $this->render($userpicture) . $fullname,
                    array('id' => 'user-picture', 'class' => 'clearfix'));
        }
        $output .= $panel->render_before_button_bits($this);

        $bcc = $panel->get_button_container_class();
        $output .= html_writer::start_tag('div', array('class' => "qn_buttons clearfix $bcc"));
        foreach ($panel->get_question_buttons() as $button) {
            $output .= $this->render($button);
        }
        $output .= html_writer::end_tag('div');

        $output .= html_writer::tag('div', $panel->render_end_bits($this),
                array('class' => 'othernav'));

        $this->page->requires->js_init_call('M.mod_quiz.nav.init', null, false,
                quiz_get_js_module());

        return $output;
    }