XtGetSelectionParameters - retrieve target parameters for a selection request
  with a single target
#include <X11/Intrinsic.h>
void XtGetSelectionParameters(Widget owner, Atom
    selection, XtRequestId request_id, Atom *type_return,
    XtPointer *value_return, unsigned long *length_return, int
    *format_return);
  - owner
- Specifies the widget that owns the specified selection.
- 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.
- type_return
- Specifies a pointer to an atom in which the property type of the
      parameters will be stored.
- value_return
- Specifies a pointer into which a pointer to the parameters are to be
      stored. A NULL will be stored if no parameters accompany the request.
- length_return
- Specifies a pointer into which the number of data elements in
      value_return of size indicated by format_return will be
      stored.
- format_return
- Specifies a pointer into which the size in bits of the parameter data in
      the elements of value_return will be stored.
XtGetSelectionParameters may only be called from within an
  XtConvertSelectionProc or from within the last call to an
  XtConvertSelectionIncrProc with a new request_id.
XtSetSelectionParameters(3)
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface