code: public HandlerRegistration addController(final I_CmsDNDController controller) {
  
          m_controllers.add(controller);
          return new HandlerRegistration() {
  
              public void removeHandler() {
  
                  m_controllers.remove(controller);
              }
          };
      }
docs: Adds another sub-controller to this controller.<p>
  
  @param controller the controller to add
  
  @return a registration object to remove the controller later