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
  ConvertSelection 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
    corresponding individual calls to XtSetSelectionParameters, and
    enclose these all within XtCreateSelectionRequest and
    XtSendSelectionRequest. XtGetSelectionValues 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