These attributes correspond to the Gadget structure's LeftEdge, TopEdge,
Width, and Height fields.  Setting any of these attributes also sets the
corresponding "relative" flag in the Gadget structure's Flags field
(respectively, GFLG_RELRIGHT, GFLG_RELBOTTOM, GFLG_RELWIDTH, and
GFLG_RELHEIGHT).  Note that the value passed in this attribute is normally
a negative LONG.  See the "Intuition Gadgets" chapter of the Amiga ROM
Kernel Reference Manual: Libraries for more information on these flags.