https://invisible-island.net/xterm/xtoolkit/
XtNameToWidget, XtWindowToWidget - translating strings to widgets or
widgets to windows
#include <X11/Intrinsic.h>
Widget XtNameToWidget(Widget reference, const char *names);
Widget XtWindowToWidget(Display *display, Window window);
display Specifies the display on which the window is defined.
names Specifies the fully qualified name of the desired widget.
reference Specifies the widget from which the search is to start.
window Specify the window for which you want the widget.
The XtNameToWidget function looks for a widget whose name is the first
component in the specified names and that is a pop-up child of refer-
ence (or a normal child if reference is a subclass of compositeWidget-
Class). It then uses that widget as the new reference and repeats the
search after deleting the first component from the specified names. If
it cannot find the specified widget, XtNameToWidget returns NULL.
Note that the names argument contains the name of a widget with respect
to the specified reference widget and can contain more than one widget
name (separated by periods) for widgets that are not direct children of
the specified reference widget.
If more than one child of the reference widget matches the name,
XtNameToWidget can return any of the children. The Intrinsics do not
require that all children of a widget have unique names. If the speci-
fied names contain more than one component and if more than one child
matches the first component, XtNameToWidget can return NULL if the sin-
gle branch that it follows does not contain the named widget. That is,
XtNameToWidget does not back up and follow other matching branches of
the widget tree.
The XtWindowToWidget function translates the specified window and dis-
play pointer into the appropriate widget instance.
X Toolkit Intrinsics – C Language Interface
Xlib - C Language X Interface
X Version 11 libXt 1.1.5.2 XtNameToWidget(3)