Hey @erlend_sh, yes! The approach is primarily based on
It is also potentially compatible with
https://socialhub.activitypub.rocks/t/fep-400e-publicly-appendable-activitypub-collections
and
(and Mastodon’s yet-to-be-merged implementation based on the latter)
I’ll be writing up an overview of the implementation soon (and clarify what I mean by things like “potentially compatible” with FEP-400e), now that it’s a fully bi-directional ActivityPub server (e.g. categories on two Discourse instances can now follow each other)