  oyOBJECT_e           type_;          /**< @private internal struct type oyOBJECT_OBSERVER_S */
  oyStruct_Copy_f      copy;           /**< copy function */
  oyStruct_Release_f   release;        /**< release function */
  oyPointer            dummy;          /**< keep to zero */

  /** a reference to the observing object */
  oyStruct_s         * observer;
  /** a reference to the to be observed model */
  oyStruct_s         * model;
  /** optional data; If no other user data is available this data will be
   *  passed with the signal. */
  oyStruct_s         * user_data;
  oyObserver_Signal_f  signal;         /**< observers signaling function */
  int                  disable_ref;    /**< disable signals reference counter
                                            == 0 -> enabled; otherwise not */
