Instead it has this crazy interface that looks like hashes of hashes but isn't (the order of the keys doesn't matter)...

The order of the keys doesn't matter in most hashes. Regexp::Common uses a tied hash to avoid compiling all of the possible regexps at compile time.

The order of keys matters in hashes of hashes. (e.g. $$hash{first_key}{second_key} ne $$hash{second_key}{first_key}). Bizarre as it may be, though, the odd way of accessing things in Regexp::Common is pretty clever.