macro_rules! delegate_keyboard {
    ($(@<$( $lt:tt $( : $clt:tt $(+ $dlt:tt )* )? ),+>)? $ty: ty) => { ... };
    ($(@<$( $lt:tt $( : $clt:tt $(+ $dlt:tt )* )? ),+>)? $ty: ty, keyboard: [$($udata:ty),* $(,)?]) => { ... };
}
Available on crate feature xkbcommon only.