it's chunk specific, there is no (hard) limit to the number of undos/redos, though it probably will start to consume memory if they get too long (especially subobjects which I'm probably going to have to treat specaly). I was considering making them survive past chunk selection, but I figured if you are moving to another chunk you are probably pretty happy with what you have, so it seemed like a good time to free the memory logging all those changes used up, and it just so happened that this was exactly the behavior my implementation got, I could make it persistent without too much pain if that would work better, but it will still be related to the current chunk, sort of how in a MDI word processor if you hit ctrl-z it will undo the currently selected document even if you just selected it after doing all sorts of stuff with something else.
