Returns the name of the geometry manager currently responsible for window, or an empty string if window isn't managed by any geometry manager. The name is usually the name of the Tcl command for the geometry manager, such as pack or place. If the geometry manager is a widget, such as canvases or text, the name is the widget's class command, such as canvas. Toplevel windows always return wm because they are managed by the window manager (even when withdrawn).