protected function addMetaTag(&$tags, $property = null, $content = null)
    {
        if (is_array($content)) {
            
            foreach ($content as $value) {
                $this->addMetaTag($tags, $property, $value);
            }
            
        } else {
            
            if ($content) {
                $tags .= $this->getMetaTag($property, $content);
            }
            
        }
    }