Thanks! I made a drawing app before, but it was only for 8x12 sprites, so I could get away with only using sset. For this, I needed something more sophisticated.
This is a pretty easy undo, but the downside is it takes up a lot of space, which could be a dealbreaker based on your needs. What I don't mention here is that the undo's also continue further into memory, into the map region - which is otherwise unused.
I haven't heard of that term, actually! It's good to know. The buttons were actually mostly based off a tweet I saw.