+ /* we cannot have a per-device cache of widgets / subwindows because
+ each visible instance needs to be a separate instance. The lowest
+ level of granularity we can get easily is the window that the
+ subwindow is in. This will fail if we attach the same subwindow
+ twice to a buffer. However, we are quite unlikely to do this,
+ especially with buttons which will need individual callbacks. The
+ proper solution is probably not worth the effort. */
+ Lisp_Object subwindow_instance_cache;