anchor.diff:  
   %% PUBLIC API
   -export([read/1]).
  +-export([fetch/2]).
   -export([write/2]).
  +
   -export([patch/2]).
  -
  --export([fetch/2]).
  +-export([add/3]).
  +-export([remove/2]).
  +-export([replace/3]).
  +-export([move/3]).
  +-export([copy/3]).
  +-export([test/3]).
   
   %% READ FILTER
   -export([rf_empty/1]).
  
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.
  