The function interface-visible-p
returns nil
if
An error is signalled if pane is not a CAPI pane (that is, it is not an instance of a subclass of element, collection or pinboard-object).
On Microsoft Windows, interface-visible-p
may return t
even though the interface is entirely obscured by another window.
CAPI User Guide and Reference Manual (Windows version) - 25 Feb 2015