"Critical concept: IRIs are opaque identifiers. You cannot infer meaning from the string pattern — only by dereferencing and inspecting the data." [1] This applies to URIs too. Sadly, almost no #ActivityPub implementations use this principle. Multi-tenant servers and simple account portability (with personal domains) would be relatively easy if they did. It is what it is...

/cc @melvincarvalho

[1] https://socialdocs.org/docs/concepts/uris-iris-linked-data/