public function ul($items = false, $parent_id = 0, $first = false)
    {
        $attrs = '';

        if (! $first && is_array($this->optionUlAttr) && count($this->optionUlAttr) > 0) {
            $attrs = $this->renderAttr($this->optionUlAttr, $parent_id);
        }
        else if($first && count($this->firstUlAttrs) > 0) {
            $attrs = $this->renderAttr($this->firstUlAttrs, $parent_id);
        }

        if (!$items) {
            return "\n".'<ul'.$attrs.'>'."\n";
        }

        return '<ul'.$attrs.'>'."\n".$items."\n".'</ul>';
    }