[Xeoncross]

For deleted items, could you not store a memo of the object in addition to the user-local changes they did?

So if you undo a change to an object that was delete by a different user, you can restore that object first to the last known state, then apply the undo?

I'm not sure this makes sense for other cases besides object deletion.

[guillaumesalles]

Yes that's good way to implement it!

But I'm still not sure this is the default behavior that we want, even it's only for deletion. I think it's more of a UX problem than an engineering problem as explained here: https://news.ycombinator.com/item?id=31682073

To take another example, for rich text editing, I don't think undoing a formatting operation on text that has been deleted at the same time should reinsert the text.