say there are three instances, A, B and C. if A is not federated with B, users from those two instances can't interact (right ?) but what if both are federated with C ? would both indirectly be able to interact ? if there is a post on instance C and a user from B comments on it, would that comment be visible on all three instances ?
Yes, comments from users on instances A and B on a post on C are visible to users on all three instances. De/federation is a way for admins of a specific instance to control which users can interact with posts on their instance. Eg: beehaw defeds sh.itjust.works so users from sh.itjust.works cannot interact with posts on beehaw. Users from both instances can interact with each other on posts on lemmy.world though.
Edit: In reality, beehaw has defederated both sh.itjust.works and lemmy.world. In my theoretical example, only sh.itjust.works has been defederated.
EDIT: I actually tested it and I'm wrong! I logged into my beehaw alt account and came to this thread but I can't see this comment as it's from sh.itjust.works. Because my comment is hidden, I also couldn't see the thread attached to this comment section so the comment thread looked empty.
Basically, every major instance that isn't sh.itjust.works, lemmy.world, lemmygrad.ml, or exploding-heads. They moderate in favor of "federate by default, defederate if it becomes a problem, refederate if the problem is addressed"
Wait, so if I am from A and comment on a post on B and a user@c from C (which A has defedrated) comments on my comment, I get a message/notification indirectly from user@c via B?
So defederation blocks direct interaction but not discourse on "neutral ground (B in this case)"?