https://invisible-island.net/xterm/xtoolkit/
XtCreateApplicationShell - create top-level widget instance
#include <X11/Intrinsic.h> Widget XtCreateApplicationShell(const char *name, WidgetClass wid- get_class, ArgList args, Cardinal num_args);
name Specifies the name of the shell. args Specifies the argument list to override any other resource specifications. num_args Specifies the number of arguments in the argument list.
The procedure XtCreateApplicationShell calls XtAppCreateShell with the application NULL, the application class passed to XtInitialize, and the default application context created by XtInitialize. This routine has been replaced by XtAppCreateShell.
XtAppCreateShell(3) X Toolkit Intrinsics – C Language Interface Xlib - C Language X Interface X Version 11 libXt 1.1.5.2 XtCreateApplicationShell(3)