def _mark_vertices(self, subdomain):
        """Mark faces/edges which are fully in subdomain.
        """
        if subdomain is None:
            is_inside = numpy.ones(len(self.node_coords), dtype=bool)
        else:
            is_inside = subdomain.is_inside(self.node_coords.T).T

            if subdomain.is_boundary_only:
                # Filter boundary
                self.mark_boundary()
                is_inside = is_inside & self.is_boundary_node

        self.subdomains[subdomain] = {"vertices": is_inside}
        return