public function registerMetaTag($options, $key = null)
    {
        if ($key === null) {
            $this->metaTags[] = $this->renderWrapperTag(Html::tag('meta', '', $options), $options);
        } else {
            $this->metaTags[$key] = $this->renderWrapperTag(Html::tag('meta', '', $options), $options);
        }
    }