From the repo readme:
   > Basically the experience is a simulation that
   > can predict its state at different points in
   > time, based on known state at other points in
   > time.
   Usually I start by designing structures for a simulation like that. The
   interface and norms end up being different than for conventional
   simulations, and there are a handful of different ways to approach it,
   which can appear to impact what's reasonable to implement later.
   I have a lot of trouble with refactoring nowadays, and can also have a
   lot of trouble with remembering things I am not immediately looking at.
   But design concerns are usually blocks: the best way to create
   something is to actually work on it!