anchor.diff:  
   
   % @fixme support creating webdav ctx with adminId
  +
  +% @fixme move ctx managemetn to other module
   
   %%%===================================================================
   %%% API
  
positive.code: %% but may not contain all required fields.
  %% @end
  %%--------------------------------------------------------------------
  -spec prepare_helper_args(name(), #{binary() := binary()}) -> args().
  prepare_helper_args(HelperName = ?S3_HELPER_NAME, Params) ->
      Transformed = maps_flatmap(fun
          (<<"hostname">>, URL) ->
  
negative.code:     {ok, Scheme, str_utils:format_bin("~s:~B", [S3Host, S3Port])}.
  
  
  -spec strip_modifiers(Fields :: [field() | optional_field()]) -> [field()].
  strip_modifiers(Fields) ->
      lists:map(fun
          ({optional, Field}) -> Field;
  