Macro tags

macro_rules! tags {
    {
        // Permit arbitrary meta items, which include documentation.
        $( #[$enum_attr:meta] )*
        $vis:vis enum $name:ident($ty:tt) $(unknown($unknown_doc:literal))* {
            // Each of the `Name = Val,` permitting documentation.
            $($(#[$ident_attr:meta])* $tag:ident = $val:expr,)*
        }
    } => { ... };
    ($name:tt, u16, $($unknown_doc:literal)*) => { ... };
    ($name:tt, $ty:tt, $($unknown_doc:literal)*) => { ... };
}