usID (USHORT)

      The identity of the graphic button that generated the notification.

    usnotifycode (USHORT)

      The notification codes that indicate what action has occurred.

      GBN_BUTTONUP

        Returned when the button is in the Up position. param2 is reserved.
      GBN_BUTTONDOWN
        Returned when the button is in the Down position. param2 is reserved.
      GBN_BUTTONHILITE
        Returned when the button is selected to the On position. param2 is reserved.
      GBN_SETFOCUS
        Returned when the button is gaining or losing focus. param2 is reserved.

      ulnotifyspec (ULONG)

        Notify command-specific information.

      ulReserved (ULONG)

        Reserved.

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