Macro get_end_field

macro_rules! get_end_field {
    ($prev_sel:expr ;) => { ... };
    ($prev_sel:expr ; (tail, $first:ident)) => { ... };
    ($prev_sel:expr ; ($($modifier:ident $(($modifier_arg:expr))?)?, $first:ident) $(, ($($rest_modifier:ident $(($rest_modifier_arg:expr))?)?, $rest:ident))*) => { ... };
}