Subtype registration has not given in the zeroconfig Oreilly

Hi, Zero Configuration Networking by Cheshire & Steinberg [O'Reilly 2006] page 65 gives an example of open._sub._mynetgame._tcp. and says that The underscore at the beginning of the subtype is not a requirement. It's optional. Stylistically you might choose to use an underscore for consistency with the service type, but you don't have to as long as you define the subtype as including or not including an underscore, and then stick with it.... but that is not discussed about how to register subtypes without underscore ... It will be great support if I can get any input on the registering subtypes to register the service .