@rmbl Oh, I see that I was confused a bit about terminology. The "Group" notion in #ActivityPub is about a group of Actors (people etc.), but we are talking here about a named "Collection" of notes/activities.
But actually GNU Social calls such collections "Groups" :-)
I'm creating descriptions and comparisons of Groups/Lists notions in different types of social networks, supported by #AndStatus, here: https://github.com/andstatus/andstatus/issues/248#issuecomment-219826572
No, I don't use IRC. That way of communication is in another Universe for me :-)