# `macro_at_most_once_rep`

The tracking issue for this feature is: TODO(mark-i-m)

With this feature gate enabled, one can use `?` as a Kleene operator meaning "0 or 1 repetitions" in a macro definition. Previously only `+` and `*` were allowed.

For example:

    # #![allow(unused_variables)]
    #![feature(macro_at_most_once_rep)]

    #fn main() {
    macro_rules! foo {
        (something $(,)?) // `?` indicates `,` is "optional"...
            => {}
    }
    #}