public function meta($name = NULL, $content = NULL) {
        if ( $name ) {
            $this->_meta[$name] = ['name' => $name, 'content' => $content];
        } else {
            return implode(PHP_EOL, array_map(function($meta) {
                return '<meta name="' . $meta['name'] . '" content="' . $meta['content'] . '" />';
            }, $this->_meta)) . PHP_EOL;
        }
    }