Usage: CLIENT <class> SET RESTRICTED [on|java|envoy|off]

This option allows you to specify which type of user you want to be able to join this client class. You can set it to java only or on for all clients.

/as client WebMaster set restricted on
/as client WebMaster set restricted off

As stated under password, if you want to restrict most of your users to the java client, you can make a restricted client class as your z-default client class and add specific exceptions higher up. You can also have this before the z-default if you want java clients to have different settings than other users.