def filter(self, **kwargs):
        """
        This method retrieve an iterable object that implements the method
        __iter__. The arguments given will compose the parameters in the
        request url.

        This method can be used compounded and recursively with query, filter,
        order, sort and facet methods.

        kwargs: valid FILTER_VALIDATOR arguments.

        return: iterable object of Works metadata

        Example:
            >>> from crossref.restful import Works
            >>> works = Works()
            >>> query = works.filter(has_funder='true', has_license='true')
            >>> for item in query:
            ...     print(item['title'])
            ...
            ['Design of smiling-face-shaped band-notched UWB antenna']
            ['Phase I clinical and pharmacokinetic study of PM01183 (a tetrahydroisoquinoline, Lurbinectedin) in combination with gemcitabine in patients with advanced solid tumors']
            ...
        """
        context = str(self.context)
        request_url = build_url_endpoint(self.ENDPOINT, context)
        request_params = dict(self.request_params)

        for fltr, value in kwargs.items():
            decoded_fltr = fltr.replace('__', '.').replace('_', '-')
            if decoded_fltr not in self.FILTER_VALIDATOR.keys():
                raise UrlSyntaxError(
                    'Filter %s specified but there is no such filter for this route. Valid filters for this route are: %s' % (
                        str(decoded_fltr),
                        ', '.join(self.FILTER_VALIDATOR.keys())
                    )
                )

            if self.FILTER_VALIDATOR[decoded_fltr] is not None:
                self.FILTER_VALIDATOR[decoded_fltr](str(value))

            if 'filter' not in request_params:
                request_params['filter'] = decoded_fltr + ':' + str(value)
            else:
                request_params['filter'] += ',' + decoded_fltr + ':' + str(value)

        return self.__class__(request_url, request_params, context, self.etiquette)