Macro special_ending_internal 

macro_rules! special_ending_internal {
    ( $( $part:ident )+ _ $next:ident $( $extra:ident )+  ) => { ... };
    ( $( $part:ident )+ _ $last_i:ident $last_v:ident ) => { ... };
    ( $( $part:ident )+ _ $last_i:literal $last_v:literal ) => { ... };
}