All DOM interfaces generate compile-time HashTables of their properties. We used to use these HashTables instead of runtime data structures, but we don't anymore. Now, we always call reifyStaticProperties to turn a HashTable into a Structure on demand. Instead of a HashTable, we should auto generate code to create a Structure, and we should eliminate the auto generated HashTables. Benefits: (1) We can more reliably disable DOM features at runtime; (2) Less boilerplate to read through, translating one (useless) format to another. (3) Shorter compile times, since we don't need to compute all the hash tables.
Another benefit: Alexey S shared anecdotal feedback that some workflows do a lot of costly reifyStaticProperties() work, which might be reduced if we reify each property individually on access, using a cacheable dictionary approach.
I wish I could plus one a bug! Probably still worth having some static constant table that can be used for the individual accesses in a general way to avoid on code size increasing, but those are just details. Time to get rid of the HashTable!