code: public WebSocketContext sendToTagged(String message, String tag, boolean excludeSelf) {
          return sendToConnections(message, tag, manager.tagRegistry(), excludeSelf);
      }
docs: Send message to all connections labeled with tag specified.
  
  @param message the message to be sent
  @param tag the string that tag the connections to be sent
  @param excludeSelf specify whether the connection of this context should be send
  @return this context