I'm not sure that it's worth rejecting this over, but I honestly think that we should _never_ use `in`. The fact that it mixes in `scope` - which is unimplemented in the vast majority of cases - is just plain dangerous. We run a serious risk of code breakage if/when `scope` is properly, fully implemented if `in` is ever used where `scope` wouldn't work. And honestly, if it were up to me, `in` would be removed from the language. Combining two attributes in one like that just invites misuse, particularly when so many people seem to like to use it as the opposite of `out` without taking into account what it actually means.