anchor.diff:  
       {error, {syntax_error, <<"field01">>}} = parse_config([{field01, "12345"}], Spec),
       
  -    {ok,[{field01, fieldXX}, {field02, false}],[{<<"unknown">>, a}]} = 
  +    {ok,[{field01, fieldXX}, {field02, false}],[{unknown, a}]} = 
           parse_config(
               [{field01, "fieldXX"}, {field02, <<"false">>}, {"unknown", a}],
               Spec),
  
positive.code: find_config(Key, Val, Rest, OK, NoOK, Syntax, Opts) ->
      case maps:get(Key, Syntax, not_found) of
          not_found ->
              parse_config(Rest, OK, [{nklib_util:to_binary(Key), Val}|NoOK], Syntax, Opts);
          Fun when is_function(Fun, 3) ->
              FunOpts = Opts#{ok=>OK, no_ok=>NoOK},
              case catch Fun(Key, Val, FunOpts) of
  
negative.code:         {ok, AtomKey} ->
              find_config(AtomKey, Val, Rest, OK, NoOK, Syntax, Opts);
          error ->
              parse_config(Rest, OK, [{Key, Val}|NoOK], Syntax, Opts)
      end;
  
  parse_config([Key|Rest], OK, NoOK, Syntax, Opts) ->
  