https://invisible-island.net/xterm/xtoolkit/
XtCreatePopupShell, XtVaCreatePopupShell - create a popup shell
#include <X11/Intrinsic.h>
Widget XtCreatePopupShell(const char *name, WidgetClass widget_class,
Widget parent, ArgList args, Cardinal num_args);
Widget XtVaCreatePopupShell(const char *name, WidgetClass widget_class,
Widget parent, ...);
args Specifies the argument list to override the resource
defaults.
name Specifies the text name for the created shell widget.
num_args Specifies the number of arguments in the argument list.
parent Specifies the parent widget.
widget_class
Specifies the widget class pointer for the created shell wid-
get.
... Specifies the variable argument list to override the resource
defaults.
The XtCreatePopupShell function ensures that the specified class is a
subclass of Shell and, rather than using insert_child to attach the
widget to the parent's children list, attaches the shell to the par-
ent's pop-ups list directly.
A spring-loaded pop-up invoked from a translation table already must
exist at the time that the translation is invoked, so the translation
manager can find the shell by name. Pop-ups invoked in other ways can
be created "on-the-fly" when the pop-up actually is needed. This
delayed creation of the shell is particularly useful when you pop up an
unspecified number of pop-ups. You can look to see if an appropriate
unused shell (that is, not currently popped up) exists and create a new
shell if needed.
XtCreateWidget(3), XtPopdown(3), XtPopup(3)
X Toolkit Intrinsics – C Language Interface
Xlib - C Language X Interface
X Version 11 libXt 1.1.5.2 XtCreatePopupShell(3)