Which toplevel window is on top?

[Richard Shann <richard rshann plus com>]

I would like to know which of the top-level windows in my application is
on top. Is there a way of doing this? I see that

------------------------------------------------------------------------
GdkEventVisibility has been deprecated since version 3.12 and should not
be used in newly-written code.

Modern composited windowing systems with pervasive transparency make it
impossible to track the visibility of a window reliably, so this event
can not be guaranteed to provide useful information.
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but is there an alternative for my (simpler) question?

Richard Shann