current_window(?Window, ?Display)

Tells whether Window is a window that is known to ProXL. If Display is specified, Window is on that display. If Window is not bound, current_window backtracks through all windows.

A window is known to ProXL if it was created by ProXL, or if it was passed to ProXL by the X server or a foreign X procedure. For example, if you call current_window/1 in a fresh ProXL session, few windows will be returned. If you call window_children/1 before calling current_window/1, many more windows will be returned, because the call to window_children/1 asks ProXL to find all the top level windows on the default screen, most of which ProXL won't have seen before.