XmDragStart — A Drag and Drop function that initiates a drag
and drop transaction

     #include <Xm/DragDrop.h>
Widget XmDragStart(
Widget widget,
XEvent *event,
ArgList arglist,
Cardinal argcount);

     XmDragStart initiates a drag operation. This routine
returns the DragContext widget that it initializes for the
associated drag transaction. The toolkit is responsible for
freeing the DragContext when the drag and drop transaction
is complete.

widget    Specifies the ID of the smallest widget and/or
          gadget that encloses the source elements selected
          for a drag operation.

event     Specifies the XEvent that triggered the drag
          operation. This event must be a ButtonPress event.

arglist   Specifies the argument list. Any XmDragContext
          resources not specified in the argument list are
          obtained from the resource database or are set to
          their default values.

argcount  Specifies the number of attribute/value pairs in
          the argument list (arglist)

     For a complete definition of DragContext and its
associated resources, see XmDragContext(3).

     Returns the ID of the DragContext widget that controls
this drag and drop transaction.  Returns NULL if the drag
cannot be initiated.

     XmDragCancel(3) and XmDragContext(3).