anchor.diff:  	{error, 400}.
   
   %% @hidden
  -filter([H | T], Acc) ->
  -	filter(T, lists:keydelete(H, 1, Acc));
  -filter([], Acc) ->
  +filter(Keys, KeyValuePairs) ->
  +	filter(Keys, KeyValuePairs, []).
  +%% @hidden
  +filter([H | T], L, Acc) ->
  +	case lists:keyfind(H, 1, L) of
  +		{H, V} ->
  +			filter(T, L, [{H, V} | Acc]);
  +		false ->
  +			filter(T, L, Acc)
  +	end;
  +filter([], _, Acc) ->
   	lists:reverse(Acc).
   
  
positive.code: 			{struct, [{name, "type"}, {value, atom_to_list(EventType)}]}],
  	AttributeChars = usage_characteristics(Attributes),
  	UsageChars = EventChars ++ AttributeChars,
  	Members = [{id, ID}, {href, Href}, {date, Date}, {type, Type},
  			{status, Status}, {usageSpecification, UsageSpec},
  			{usageCharacteristic, {array, UsageChars}}],
  	{struct, filter(Filters, Members)};
  usage_aaa_acct(Events, Filters) when is_list(Events) ->
  	usage_aaa_acct(Events, Filters, []).
  %% @hidden
  
negative.code: 	RequestChars = usage_characteristics(RequestAttributes),
  	ResponseChars = usage_characteristics(ResponseAttributes),
  	UsageChars = EventChars ++ RequestChars ++ ResponseChars,
  	ObjectMembers = [{id, ID}, {href, Href}, {date, Date}, {type, Type},
  			{status, Status}, {usageSpecification, UsageSpec},
  			{usageCharacteristic, {array, UsageChars}}],
  	{struct, filter(["id", "href"] ++ Filters, ObjectMembers)};
  usage_aaa_auth(Events, Filters) when is_list(Events) ->
  	usage_aaa_auth(Events, Filters, []).
  %% @hidden
  