@classmethod
def preferred_ordinal(cls, attr_name):
    """
        Returns an ordering value for a particular attribute key.

        Unrecognized attributes and OIDs will be sorted lexically at the end.

        :return:
            An orderable value.

        """
    attr_name = cls.map(attr_name)
    if attr_name in cls.preferred_order:
        ordinal = cls.preferred_order.index(attr_name)
    else:
        ordinal = len(cls.preferred_order)
    return ordinal, attr_name
