code: public static Builder newBuilder(SubnetworkId subnetworkId, NetworkId network, String ipRange) {
      return new BuilderImpl(subnetworkId, network, ipRange);
    }
docs: Returns a builder for a {@code SubnetworkInfo} object given the identity of the subnetwork, the
  identity of the network this subnetwork belongs to and the range of IPv4 addresses owned by
  this subnetwork. {@code ipRange} must be a CIDR specification, for example: {@code
  192.168.0.0/16}.
  
  @see <a href="https://wikipedia.org/wiki/Classless_Inter-Domain_Routing">CIDR</a>