Add rel to gallery

Hello.

Information for those who could not add rel= for grouping. Groups exactly within the post, useful on the listing pages.

Here is a solution I came up with.

Add to functions.php file

add_filter('wp_get_attachment_link', 'gallery_add_rel');
function gallery_add_rel($link) {
global $post;
return str_replace('<a href', '<a rel="gel' . $post->ID . '" href', $link);
}