This message allows the window under the mouse pointer to determine if the object or objects currently being dragged can be dropped.

param2 is the pointing device pointer location.

param1
     PDRAGINFO  pDraginfo    /*  Pointer to the DRAGINFO structure representing the object being dragged. */

param2
     SHORT      sxDrop       /*  X-coordinate of the pointing device pointer in desktop coordinates. */
     SHORT      syDrop       /*  Y-coordinate of the pointing device pointer in desktop coordinates. */

returns
     USHORT     usDrop       /*  Drop indicator. */
     USHORT     usDefaultOp  /*  Target-defined default operation. */