Another approach is to use an anonymous function. Hey, it's even a closure! 
$mw->Button(
    -text=>"About...", 
    -command=> sub { do_toplevel($mw) } }
)-> pack (-side=>"bottom");

[download]
It's the same sort of thing you do later on for the Close button in do_toplevel(). :)

In reply to Re: Modal Tk Toplevel/Passing a MainWindow by chromatic
in thread Modal Tk Toplevel/Passing a MainWindow by slojuggler

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