anchor.diff:          error -> error
       end;
   
  -spec({atoms, List}, Val) ->
  +spec({atom, List}, Val) ->
       case to_existing_atom(Val) of
           {ok, Atom} ->
               case lists:member(Atom, List) of
  
positive.code:         field08 => host,
          field09 => host6,
          field10 => fun parse_fun/3,
          field11 => [{atoms, [a]}, binary],
          field12 => {list, atom},
          field13 => module,
          fieldXX => invalid
  
negative.code:     Spec = #{
          field01 => atom,
          field02 => boolean,
          field03 => {atom, [a, b]},
          field04 => integer,
          field05 => {integer, 1, 5},
          field06 => string,
  