The predicate for whether the interface containing a pane is visible.
A CAPI pane.
is not associated with any interface, or
is associated with an interface which is not displayed, or
is associated with an interface which is minimized or iconified, or
is known to be fully obscured by other windows. This can happen on Motif, but is not detected on Microsoft Windows.
An error is signalled if
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 (Macintosh version) - 25 Feb 2015