It's important, but I purposely stepped around this to not complicate things.

In truth, the only likely situation from these rules is hand-copying configuration then manually transposing. This isn't likely to happen in really hot code paths.

This is the one place where JS helps us because lazy typers are encouraged to return object literals from factory functions and the return will almost always be one object returned at the bottom of the function.

It also (intentionaly) bypasses manually adding elements to an object directly after the object is instantiated. In truth, doing this consistently and directly after it is created can usually be optimized too, but not necessarily and describing this also complicates things (and varies from one JIT to the next).