This attribute corresponds to the system gadget type portion of the
gadget's Gadget.GadgetType fields.  This attribute is any one of the
following flags (from <intuition/intuition.h>):

    GTYP_SIZING, GTYP_WDRAGGING, GTYP_SDRAGGING, GTYP_WUPFRONT,
    GTYP_SUPFRONT, GTYP_WDOWNBACK, GTYP_SDOWNBACK, GTYP_CLOSE

See the "Intuition Gadgets" chapter of the Amiga ROM Kernel Reference
Manual: Libraries for more information.