anchor.diff:              end
       end.
   
  +%% @doc Returns a ReadFilter which tests the existens of a value
  +%% in a stored JSON object.
  +-spec get_rf_test_fun(path(), client_value()) -> prbr:read_filter().
  +get_rf_test_fun(Path, Value) ->
  +    fun
  +        (prbr_bottom) -> ?NON_EXIST_VAL;
  +        (Obj)         ->
  +            case dotto:test(Obj, Path, Value) of
  +                {ok, Result} -> Result;
  +                Any -> Any
  +            end
  +    end.
   
   %% %%%%%%%%%%%%%%%%
   %% CONTENT CHECK
  
positive.code: patch(Key, Patch) ->
      write_helper(Key, Patch, fun ?MODULE:wf_patch/3).
  
  
  %% %%%%%%%%%%%%%%%%
  %% READ FILTER
  
negative.code:                             end)
              end
      end.
  
  %% @doc Helper that unpacks a list of errors if this list contains only one
  %% error. Does nothing otherwise.
  -spec unpack_if_error_list(any()) -> any().
  unpack_if_error_list({error, [{error, Reason}]}) -> {error, Reason};
  unpack_if_error_list(Any) -> Any.
  