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 1.1.5.2 XtHooksOfDisplay(3)