https://invisible-island.net/xterm/xtoolkit/
XtSetSelectionParameters - specify target parameters for a selection
request with a single target
#include <X11/Intrinsic.h>
void XtSetSelectionParameters(Widget requestor, Atom selection, Atom
type, XtPointer value, unsigned long length, int format);
requestor Specifies the widget making the request. Must be of class
Core or any subclass thereof.
selection Specifies the atom that names the selection.
type Specifies the type of the property in which the parameters
will be passed.
value Specifies a pointer to the parameters.
length Specifies the number of elements containing data in value,
each element of a sized indicated by format.
format Specifies the size in bits of the data in the elements of
value.
The specified parameters will be copied and stored in a new property of
the specified type and format on the requestor's window. To initiate a
selection request with a target and these parameters, a subsequent call
to XtGetSelectionValue or to XtGetSelectionValueIncremental specifying
the same requestor widget and selection atom will generate a ConvertSe-
lection request referring referring to the property containing the
parameters. If XtSetSelectionParameters is called more than once with
the same widget and selection without a call to specify a request, the
most recently specified parameters are used in the subsequent request.
The possible values of format may be 8, 16, or 32. If the format is 8,
the elements of value are assumed to be sizeof(char); if 16,
sizeof(short); if 32, sizeof(long).
To generate a MULTIPLE target request with parameters for any of the
multiple targets of the selection request, precede individual calls to
XtGetSelectionValue and XtGetSelectionValueIncremental with correspond-
ing individual calls to XtSetSelectionParameters, and enclose these all
within XtCreateSelectionRequest and XtSendSelectionRequest. XtGetSe-
lectionValues and XtGetSelectionValuesIncremental cannot be used to
make selection requests with parameterized targets.
XtGetSelectionParameters(3)
X Toolkit Intrinsics – C Language Interface
Xlib - C Language X Interface
X Version 11 libXt 1.1.5.2 XtSetSelectionParameters(3)