XtGetSelectionRequest - retrieve the event that triggered the
  XtConvertSelectionProc
#include <X11/Intrinsic.h>
XSelectionRequestEvent* XtGetSelectionRequest(Widget w,
    Atom selection, XtRequestId request_id);
  - w
- Specifies the widget.
- selection
- Specifies the selection being processed.
- request_id
- Specifies the requestor id in the case of incremental selections, or NULL
      in the case of atomic transfers.
XtGetSelectionRequest may only be called from within an
  XtConvertSelectionProc procedure and returns a pointer to the
  SelectionRequest event that caused the conversion procedure to be
  invoked. Request_id specifies a unique id for the individual request in
  the case that multiple incremental transfers are outstanding. For atomic
  transfers, request_id must be specified as NULL. If no
  SelectionRequest event is being processed for the specified
  widget, selection, and request_id,
  XtGetSelectionRequest returns NULL.
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface