Tk_MainWindow - find the main window for an application
SYNOPSIS
#include <tk.h>
Tk_Window
Tk_MainWindow(interp)
ARGUMENTS
Tcl_Interp *interp (in/out)
Interpreter associated with the application.
DESCRIPTION
If interp is associated with a Tk application then Tk_MainWindow
returns the application's main window.
If there is no Tk application associated with interp then
Tk_MainWindow returns NULL and leaves an error message
in interp->result.