anchor.diff:  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>()
  
positive.code:         isProgressFrame(parser: 'letter or digit expected', position: 3),
          isProgressFrame(parser: 'letter or digit expected', position: 4),
          isProgressFrame(parser: 'letter or digit expected', position: 5),
        ]);
      });
      test('failure', () {
  
negative.code:         isProfileFrame(parser: 'letter expected', count: 1),
        ]);
      });
      test('labeled', () {
        final frames = <ProfileFrame>[];
        final parser = profile(labeledIdentifier,
            output: frames.add, predicate: (parser) => parser is LabeledParser);
        expect(parser.parse('ab123').isSuccess, isTrue);
        expect(frames, [
          isProfileFrame(parser: 'remaining', count: 1),
          isProfileFrame(parser: 'first', count: 1),
        ]);
      });
      test('failure', () {
        final frames = <ProfileFrame>[];
        final parser = profile(identifier, output: frames.add);
  