https://invisible-island.net/xterm/xtoolkit/
XtGetSelectionRequest - retrieve the event that triggered the XtCon-
vertSelectionProc
#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 selec-
tions, or NULL in the case of atomic transfers.
XtGetSelectionRequest may only be called from within an XtConvertSelec-
tionProc procedure and returns a pointer to the SelectionRequest event
that caused the conversion procedure to be invoked. Request_id speci-
fies 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
X Version 11 libXt 1.1.5.2 XtGetSelectionRequest(3)