The docs of Win32::GUI say as follows:

Non-owned windows

Every window, even windows not created by your Perl script, can be referenced by Win32::GUI; all you need to know is its "handle", a numerical value that identifies that window. Many functions in the Win32::GUI package return such handles, as for example:

    $First = Win32::GUI::GetForegroundWindow();
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This value can then be passed to any function that requires a window object; but of course, not being an object, you can't call it as a method:

    Win32::GUI::Hide($First); # correct
    $First->Hide();           # wrong
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Should you need to know the numerical handle of a window created by Win32::GUI, it is stored in its -handle key (this is the value that almost all function really use):

    print "Window handle is $Window->{-handle} \n";
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