Thanks—I meant “formal” as in “formal grammar”, not that it wasn’t described in the published protocol. As in, there’s nothing in the protocol’s explicit form that distinguishes between this implied meaning and a real extra recipient—so it simplifies the parsing but adds an extra post-parsing step.

Why not a binary flag or something? Is it just to avoid making it a formal part of the protocol?

Does ActivityPub really send copies of all activities to www.w3.org?

I believe that an out-of-the-box lemmy instance will remove deleted content from federated instances automatically.

My point is just that site maintainers can modify the software to do whatever they want, or run software that implements ActivityPub but whose functionality is completely different from that of lemmy.

As another commenter has said, this is likely just a feature of the interface and not a reflection of what other users see.

But you should keep in mind that, due to the nature of federation, your posts are copied to all other instances that are federated with yours—which in theory includes not just lemmy instances but any software implementing the ActivityPub protocol. Whether those instances actually remove posts you’ve marked as deleted is up to their discretion.