The question was about backward compatibility. I argued for it. I'm not sure how you saw me saying that we should do nothing. It is certainly not my position. Perhaps it is my use of "preservation" that suggested more than ability to consume existing change-tracked documents as reliably as possible. I did not mean more than reliable backward (although isn't it upward compatibility, technically? Maybe we need to clarify the terminology). We should certainly take into consideration of the impact of additional (and corrected) provisions on down-level implementations, but I wasn't thinking about that here. - Dennis