public function end($content = null, $options = []) {
        $this->_lastPanelClosed = true;
        $res = '';
        $res .= $this->_cleanCurrent();
        if ($content !== null) {
            $res .= $this->footer($content, $options);
        }
        $res .= $this->formatTemplate('panelEnd', []);
        $this->_states->pop();
        return $res;
    }