Macro define_key 

macro_rules! define_key {
    ($ty:ty,
        $name_vis:vis $name:ident
        $(, opt : $opt_vis:vis $opt_name:ident)?
        $(, rng : $rng_vis:vis $rng_name:ident)?
        $(, dsp : $dsp_name:expr)?
    ) => { ... };
    ($all_vis:vis, $ty:ty,
        $name:ident
        $(, opt : $opt_name:ident)?
        $(, rng : $rng_name:ident)?
        $(, dsp : $dsp_name:expr)?
    ) => { ... };
}