def add_holes(self, holes_list, make_ccw=True):
        """
        Add holes to the holes list.
        
        :param holes_list: Polygons that will be treated as holes.
        :type holes_list: list or pyny.Polygon
        :param make_ccw: If True, points will be sorted ccw.
        :type make_ccw: bool
        :returns: None
        
        .. note:: The holes can be anywhere, not necesarily on the 
            surface.
        """
        if type(holes_list) != list: holes_list = [holes_list]
        self.holes += [Polygon(hole, make_ccw) for hole in holes_list]