How to use the cerberus.schema.DefinitionSchema function in Cerberus

def __init_processing(self, document, schema=None):
        self._errors = errors.ErrorList()
        self.recent_error = None
        self.document_error_tree = errors.DocumentErrorTree()
        self.schema_error_tree = errors.SchemaErrorTree()
        self.document = copy(document)
        if not self.is_child:
            self._is_normalized = False

        if schema is not None:
            self.schema = DefinitionSchema(self, schema)
        elif self.schema is None:
            if isinstance(self.allow_unknown, Mapping):
                self._schema = {}
            else:
                raise SchemaError(errors.SCHEMA_ERROR_MISSING)
        if document is None:
            raise DocumentError(errors.DOCUMENT_MISSING)
        if not isinstance(document, Mapping):
            raise DocumentError(errors.DOCUMENT_FORMAT.format(document))
        self.error_handler.start(self)

def schema(self, schema):
        if schema is None:
            self._schema = None
        elif self.is_child or isinstance(schema, DefinitionSchema):
            self._schema = schema
        else:
            self._schema = DefinitionSchema(self, schema)

def __init_processing(self, document, schema=None):
        self._errors = errors.ErrorList()
        self.recent_error = None
        self.document_error_tree = errors.DocumentErrorTree()
        self.schema_error_tree = errors.SchemaErrorTree()
        self.document = copy(document)
        if not self.is_child:
            self._is_normalized = False

        if schema is not None:
            self.schema = DefinitionSchema(self, schema)
        elif self.schema is None:
            if isinstance(self.allow_unknown, Mapping):
                self._schema = {}
            else:
                raise SchemaError(errors.SCHEMA_ERROR_MISSING)
        if document is None:
            raise DocumentError(errors.DOCUMENT_MISSING)
        if not isinstance(document, Mapping):
            raise DocumentError(errors.DOCUMENT_FORMAT.format(document))
        self.error_handler.start(self)

def __new__(cls, *args, **kwargs):
        if 'SchemaValidator' not in globals():
            global SchemaValidator
            SchemaValidator = validator_factory('SchemaValidator', SchemaValidatorMixin)
            types_mapping = SchemaValidator.types_mapping.copy()
            types_mapping.update(
                {
                    'callable': TypeDefinition('callable', (Callable,), ()),
                    'hashable': TypeDefinition('hashable', (Hashable,), ()),
                }
            )
            SchemaValidator.types_mapping = types_mapping

        return super(DefinitionSchema, cls).__new__(cls)

def _expand_definition(cls, definition):
        return DefinitionSchema.expand({0: definition})[0]

def allow_unknown(self, value):
        if not (self.is_child or isinstance(value, (bool, DefinitionSchema))):
            DefinitionSchema(self, {'allow_unknown': value})
        self._config['allow_unknown'] = value