The rebasing step is indeed a transformation. Some info in the "rebasing" link here [1].
Unlike traditional Operational Transformation, though, there are no "transformation properties" [2] that this rebasing needs to satisfy. (Normally a central-server OT would need to satisfy TP1, or else users may end up in inconsistent states.) Instead, the rebased operations just need to "make sense" to users, i.e., be a reasonable way to apply your original edit to a slightly-further-ahead state. ProseMirror has this sort of rebasing built in, via its step mappings, which lets the collaboration-specific parts of the algorithm look very simple - perhaps deceptively so.
Author here, just chiming in to say that Matt has an actual PhD on the subject so rather than explain it worse, I will just let him say the probably-actually-correct thing here.
Unlike traditional Operational Transformation, though, there are no "transformation properties" [2] that this rebasing needs to satisfy. (Normally a central-server OT would need to satisfy TP1, or else users may end up in inconsistent states.) Instead, the rebased operations just need to "make sense" to users, i.e., be a reasonable way to apply your original edit to a slightly-further-ahead state. ProseMirror has this sort of rebasing built in, via its step mappings, which lets the collaboration-specific parts of the algorithm look very simple - perhaps deceptively so.
[1] https://prosemirror.net/docs/guide/#collab [2] https://en.wikipedia.org/wiki/Operational_transformation#Tra...