BUR #18044 has been rejected.
undeprecate upside_down
create alias upside_down -> upside-down
Isn't an alias better than deprecation in this case? The suggestions should give you the proper one, but if you type quickly or absent mindedly, or if suggestions are slow to load for whatever reason, you may end up using upside_down on accident and having to correct it after the fact. (yes I'm making this because it just happened to me kek)