Big things today, but mostly pain :') Because of the levels being in progressive stages, the way they're saved to and loaded from files needs to be ordered - which was irritating, because the data language didn't support arrays of objects yet! Like JSON, YAML, Lua tables etc. there's an 'object' notation which is internally a hashmap, and an 'array' system that is contiguous and preserves the order as declared.
There was lots of changing around because before today all array elements were unquoted strings, always (nothing mixed, or even anything not-string!). But we're here now, files can be written to and read from in the way the game requires.