Design rationale document

[hatcat]

I think we need a design rationale document. Most proposals I've seen include choices and reasons for particular motivations, whereas our paper is presented as a fait accompli. There are MANY design decisions in this paper, and I seem to spend a lot of time explaining why things are done a certain way.

I imagine this is something only you could write, but I'm happy to pitch in if there's a way I can make this happen.