Macro literal 

macro_rules! literal {
    ($(#[$attr:meta])* $name:ident($type:tt) = $value:literal) => { ... };
    ($(#[$attr:meta])* $name:ident($serde_from:tt => $type:tt) = $value:literal) => { ... };
    ($(#[$attr:meta])* $name:ident(&$type:tt) = $value:literal) => { ... };
    ($(#[$attr:meta])* $name:ident($serde_from:tt => &$type:tt) = $value:literal) => { ... };
    (@ $(#[$attr:meta])*  $name:ident($serde_from:tt => $type:tt) = $value:literal) => { ... };
}