[scofalik]

Interesting question! Actually, at the moment we don’t :).

We did some testing to see how big this issue is and it turned out that it's not dramatic. The main difficulty with graveyard purging is that you need to keep the undo in mind. Elements in the graveyard are used for undo, so garbage collecting will have to be strictly connected with limiting undo steps.

Add to that collaborative changes and it becomes a tougher problem. Therefore, we'd probably start from what seems to be the safest option – trimming the history stack and implementing a garbage collector that goes through all the possible reference points.

[fovc]

Yup. Ran into the same thing.

Another Q for you if you're still around: did you have to make any changes to your algorithm for when it's running through the undo queue, or is it basically the same thing but in reverse? I found some operations could better preserve intention with some adjustments to the undo transform

[scofalik]

Oh, don't get me started on modifications we needed to do to make undo look reasonable ... :) At first, we thought that undo is the same thing as collaboration but... nope.

The crucial difference is that with undo you have a context (old document state). With collaboration, you don't. So if both users put a character at the same position, in collaboration the order of output doesn't matter (and can't be solved really). In undo it does, because a user remembers what was the order of the letters before they made a change.

[fovc]

We should compare notes some time :) Sounds like we had to solve a lot of the same issues and the dearth of info on this topic is surprising!