anchor.diff:           allow_missing_post/2,
            known_methods/2,
            allowed_methods/2,
  +         options/2,
            content_types_provided/2,
            content_types_accepted/2,
            delete_resource/2,
  
positive.code:             {ok, Req1} = cowboy_req:reply(500, [], stringify(Reason), Req0),
              {stop, Req1, State};
          ok ->
              {true, Req0, State}
      end.
  
  content_types_accepted(Req, State) ->
  
negative.code:     {true, Req, State}.
  
  known_methods(Req, State) -> 
      {[<<"OPTIONS">>,<<"GET">>,<<"POST">>,<<"DELETE">>], Req, State}.
  
  allowed_methods(Req, State) ->
      {[<<"OPTIONS">>,<<"GET">>,<<"POST">>,<<"DELETE">>], Req, State}.
  
  content_types_provided(Req, State) ->
      {[{<<"application/json">>, handle_json}], Req, State}.
  
  options(Req0, State) ->
      Req1 = cowboy_req:set_resp_header(<<"Access-Control-Allow-Headers">>,
                                                      <<"content-type">>, Req0),
      {ok, Req1, State}.
  
  resource_exists(Req0, #{identifier := Identifier} = State) ->
      case dbyr_identifier:get_metadata(Identifier) of
  