anchor.diff:              parser: 'SequenceParser', level: 0, result: isSuccessContext()),
         ]);
       });
  +    test('labeled', () {
  +      final events = <TraceEvent>[];
  +      final parser = trace(labeledIdentifier,
  +          output: events.add, predicate: (parser) => parser is LabeledParser);
  +      expect(parser.parse('ab123').isSuccess, isTrue);
  +      expect(events, [
  +        isTraceEvent(parser: 'first', level: 0),
  +        isTraceEvent(
  +            parser: 'first', level: 0, result: isSuccessContext(value: 'a')),
  +        isTraceEvent(parser: 'remaining', level: 0),
  +        isTraceEvent(
  +            parser: 'remaining',
  +            level: 0,
  +            result: isSuccessContext(value: 'b123'.split(''))),
  +      ]);
  +    });
       test('failure', () {
         final events = <TraceEvent>[];
         final parser = trace(identifier, output: events.add);
  
positive.code:         isProfileFrame(parser: 'letter expected', count: 1),
        ]);
      });
      test('failure', () {
        final frames = <ProfileFrame>[];
        final parser = profile(identifier, output: frames.add);
  
negative.code: import 'test_utils.dart';
  
  final identifier = letter() & word().star();
  final labeledIdentifier =
      letter().labeled('first') & word().star().labeled('remaining');
  
  Matcher isProfileFrame({required String parser, int count = 0}) =>
      isA<ProfileFrame>()
  