macro_rules! idref {
(unchecked $id1:ident : $id2:ident) => { ... };
(unchecked $id1:expr, $id2:expr) => { ... };
(unchecked $id:ident) => { ... };
(unchecked $id:expr) => { ... };
($id1:ident, $id2:ident) => { ... };
($id1:expr, $id2:expr) => { ... };
}