Macro new_selector 

macro_rules! new_selector {
    (
        $(
            $(#[$meta: meta])*
            $(-($($r:tt)*)[$class1: ident $($sel1:tt)*])?
            $(+($($r2:tt)*)[$class2: ident $($sel2:tt)*])?
            unsafe extern "C" fn $name: ident ($($arg:ident: $ty: ty),* $(,)?) $(->$ret:ty)? $body: block
        )*
    ) => { ... };
}