In #690 we added regionCode...

@aestes, @rsolomakhin, @zouhir, looks Chrome, Safari, and Edge don't expose the regionCode attribute. In Firefox, we implement it (just the IDL), but haven't mapped it to actual ISO3166-2 regions in the UI... thus, it just always returns "".

For the purpose of CR, should we keep it in the spec or move it out?... or do any of you plan to implement it too sometime soon?