TIL: #Mastodon specifically treats actor URIs with the pattern https://<domain>/actor as instance actors

Where are you seeing this?

Mastodon does serve its instance actor as /actor, however it doesn’t actually track the “instance actor” as a concept, because there’s actually no way to do so. fep-2677 doesn’t define one, it just says the instance actor must be an Application, and adds a reference to that actor to NodeInfo.

That is, from the actor document alone, there is no way to know if it is the “instance actor” (remembering too that AP doesn’t have any notion of an “instance” or “server")

Likewise, internally in Mastodon, the instance actor record will have the ID of -99.