@gardevoir the activitypub protocol has separate addressee and body fields, so you can in theory say "send this to X Y and Z" and then not mention X, Y, or Z anywhere in the body of the post, and any standard-compliant AP implementation will handle it properly (X, Y, and Z will get the post in their notifications)
For some reason (maybe to be like twitter, i assume?) mastodon doesn't do this, instead just finding anyone mentioned in the body and copying that to the addressee field
-F/R