I'd assumed that the updating of the B3 dict takes place at runtime, either during module initialisation or lazily at the first call (that is, roughly as late a

I'd assumed that the updating of the B3 dict takes place at runtime, either during module initialisation or lazily at the first call (that is, roughly as late as possible -- certainly, well after the wheel was built), just as a perf optimisation. But then I realised the code does (and must do) a lookup in the B3 table for each character anyway, so there doesn't seem to be any point. I suppose it means they can load the full 3.2.0 table once, use it to discover the exceptions and then immediately evict it from memory, keeping only the presumably smaller and faster-to-query B3 table of exceptions, but this seems pretty marginal...