https://invisible-island.net/xterm/xtoolkit/
XtHooksOfDisplay - external agent access points
#include <X11/Intrinsic.h>
Widget XtHooksOfDisplay(Display* display);
display Specifies the desired display.
The class of this object is a private, implementation dependent, sub-
class of Object. The hook object has no parent. The resources of this
object are the callback lists for hooks and the read-only resources for
getting a list of parentless shells.
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface
X Version 11 libXt 1.3.1 XtHooksOfDisplay(3)