static JWindow makeUnimportantWindow(final Component c) {
  ret swing(func -> JWindow {
    Map map = cast vm_generalMap_get("unimportant windows");
    if (map == null)
      vm_generalMap_put("unimportant windows", map = (Map) callJavaX('newWeakHashMap));
    JWindow w = makeWindow(c);
    map.put(w, true);
    ret w;
  });
}