Interestingly, this project makes use of a conflict-free replicated data type (CRDT) data structure [1]. All the information on where they use this can be found on their page detailing their approach to async plugins and undo[2].
[1] https://en.wikipedia.org/wiki/Conflict-free_replicated_data_...
[2] http://google.github.io/xi-editor/docs/crdt.html