Create multiple galleries with lightbox action

I am trying to create multiple galleries on the same page. featherlight plugin has gallery function but all images on the page will be in the same gallery.
How difficult would be to add another parameter to lightbox action so it generates rel attributes like rel=“lightbox-nn” where nn is a counter?

It doesn’t need to be automatic. A call like this would be fine:


Where 1 will be concatenated with rel:


Well, looks like this forum is dead…
Right now I will do it using init script of my custom lightbox plugin.