on-superwindow-enable in window<%>
Called via the event queue whenever the enable state of a window has
changed, either through a call to the window's
enable method, or through the enabling/disabling of one of the window's
ancestors. The method's argument indicates whether the window is now
enabled or not.
This method is not called when the window is initially created; it is called only after a change from the window's initial enable state. Furthermore, if an enable notification event is queued for the window and it reverts its enabled state before the event is dispatched, then the dispatch is canceled.
If the enable state of a window's ancestor changes while the window is
deleted (e.g., because it was removed with
delete-child), then no enable events are queued for the deleted window. But if
the window is later re-activated into an enable state that is
different from the window's state when it was de-activated, then an
enable event is immediately queued.