def _discover_params(cls):
        """
        Returns a dict where filter keyword is key, and class is value.
        To handle param alias (maxRecords or max_records), both versions are
        added.
        """

        try:
            return cls.filters
        except AttributeError:
            filters = {}
            for param_class_name in dir(cls):
                param_class = getattr(cls, param_class_name)
                if hasattr(param_class, 'kwarg'):
                    filters[param_class.kwarg] = param_class
                    filters[param_class.param_name] = param_class
            cls.filters = filters
        return cls.filters