anchor.diff:    final serializedAgain =
         standardSerializers.serializeWith(Account.serializer, value);
     assert(serializedAccount.toString() == serializedAgain.toString());
  +
  +  // In this second example we don't know the type we want to
  +  // serialize/deserialize, so it has to be specified on the wire.
  +  final serializedAccountWithDiscriminator = {
  +    r'$': 'Account',
  +    'id': 3,
  +    'name': 'John Smith',
  +    'keyValues': {
  +      'visited': 1732,
  +      'active': true,
  +      'email': 'john.smith@example.com',
  +      'tags': [74, 123, 4001],
  +      'preferences': {
  +        'showMenu': true,
  +        'skipIntro': true,
  +        'colorScheme': 'light',
  +      }
  +    }
  +  };
  +
  +  // We don't have to specify the type when deserializing.
  +  final value2 =
  +      standardSerializers.deserialize(serializedAccountWithDiscriminator);
  +  print(value2);
  +  assert(value == value2);
  +
  +  // We don't have to specify the type when serializing.
  +  final serializedAgain2 = serializers.serialize(value2);
  +  assert(serializedAccountWithDiscriminator.toString ==
  +      serializedAgain2.toString());
   }
  
positive.code:   // See chat_example and end_to_end_test for more complex usage!
  }
  
  /// Example of using StandardJsonPlugin.
  ///
  /// The plugin changes the built_value serialization format to the Map-based
  /// format used by most JSON APIs.
  
negative.code: /// a `discriminator` field. By default this field is called `$`; you can pass
  /// a different name to the `StandardJsonPlugin` constructor. If the wire
  /// format should not contain the type name, you must instead explicitly
  /// specify which type to serialize/deserialize. Both cases are shown below.
  void standardJsonExample() {
    final standardSerializers =
        (serializers.toBuilder()..addPlugin(new StandardJsonPlugin())).build();
  
    // In this first example we know the type we want to serialize/deserialize,
    // so the type is not mentioned on the wire.
    final serializedAccount = {
      'id': 3,
      'name': 'John Smith',
  