See https://dlang.org/spec/function.html#parameters
I also noticed Walter removed `in` in this PR: https://github.com/dlang/phobos/pull/6561
Should it be deprecated (not necessarily removed) to guide users towards a more consistent and idiomatic usage of the language? Also, if there are fewer usages, it will make it much easier to redefine `in` to something useful in the future.
Mike
