The reserved values can be used as tags in outer enum types. For example `Option<bool>` might encode `None` as 2. If you did `Some(transmute::<bool>(2))` it'd t

The reserved values can be used as tags in outer enum types. For example `Option<bool>` might encode `None` as 2. If you did `Some(transmute::<bool>(2))` it'd turn into `None`.