Returns the document normalized according to the specified rules
        of a schema.

        :param document: The document to normalize.
        :type document: any :term:`mapping`
        :param schema: The validation schema. Defaults to :obj:`None`. If not
                       provided here, the schema must have been provided at
                       class instantiation.
        :type schema: any :term:`mapping`
        :param always_return_document: Return the document, even if an error
                                       occurred. Defaults to: ``False``.
        :type always_return_document: :class:`bool`
        :return: A normalized copy of the provided mapping or :obj:`None` if an
                 error occurred during normalization.

def normalized(self, document, schema=None, always_return_document=False):
        """ Returns the document normalized according to the specified rules
        of a schema.

        :param document: The document to normalize.
        :type document: any :term:`mapping`
        :param schema: The validation schema. Defaults to :obj:`None`. If not
                       provided here, the schema must have been provided at
                       class instantiation.
        :type schema: any :term:`mapping`
        :param always_return_document: Return the document, even if an error
                                       occurred. Defaults to: ``False``.
        :type always_return_document: :class:`bool`
        :return: A normalized copy of the provided mapping or :obj:`None` if an
                 error occurred during normalization.
        """
        self.__init_processing(document, schema)
        self.__normalize_mapping(self.document, self.schema)
        self.error_handler.end(self)
        if self._errors and not always_return_document:
            return None
        else:
            return self.document