This Tk command marks window as being part of the same group of windows as pathName (another toplevel widget), or queries what group window is in; if it is not in the same group as another widget (or if it is the group leader?) the result will be the empty string. Grouped windows are managed together (i.e., iconified and deiconified together, possibly kept together in the stacking order, etc.) in a way that is up to the window manager to determine; this is formally just a hint.