https://groups.google.com/forum/?fromgroups=#!topic/comp.lang.perl.tk/-mMmqk43nhE

##</code><code>##

use warnings 'all';
use strict;
use Tk;

our ($main_window,$main_frame,$list1,$list2);

$main_window  = MainWindow->new();
$main_frame   = $main_window->Frame->pack();

$list1        = $main_frame->Listbox()->pack();
$list1->insert('end','list1');

$list2        = $main_frame->Listbox()->pack();
$list2->insert('end','list2');
$list2->selectionSet(0);

print $list2->selectionIncludes(0),"\n";
$list1->selectionSet(0 );
print $list2->selectionIncludes(0),"\n";

MainLoop;