code: public void requestBroadcast (String message)
      {
          message = filter(message, null, true);
          if (message == null) {
              displayFeedback(_bundle, MessageBundle.compose("m.broadcast_failed", "m.filtered"));
              return;
          }
          _cservice.broadcast(message, new ChatService.InvocationListener() {
              public void requestFailed (String reason) {
                  reason = MessageBundle.compose("m.broadcast_failed", reason);
                  displayFeedback(_bundle, reason);
              }
          });
      }
docs: Requests to send a site-wide broadcast message.
  
  @param message the contents of the message.