code: func (m *subMenu) PopupInWindow(w *Window, o *MenuPopupOptions) (err error) {
  	if err = m.isActionable(); err != nil {
  		return
  	}
  	var e = Event{Name: EventNameSubMenuCmdPopup, TargetID: m.id, MenuPopupOptions: o}
  	if w != nil {
  		e.WindowID = w.id
  	}
  	_, err = synchronousEvent(m.c, m, m.w, e, EventNameSubMenuEventPoppedUp)
  	return
  }
docs: // PopupInWindow pops up the menu as a context menu in the specified window