This is in preparation for throwing errors (with diagnostic information) on
yet-to-be-supported tokens, so that I can confidently compile individual
packages without worrying that something is just being ignored.
This makes obvious that `ele_parse!` had a different design in mind
previously, and it's now resulting in a lot of boilerplate; I'll address
that in the future once I'm certain requirements have been settled on, since
I've spent far too much time on it to waste more.
DEV-13708