But personally, for this sort of thing, I'd use the "grid" geometry manager:

#!/usr/bin/perl
use strict;
use warnings;
use Tk qw/tkinit/;

my $mw = Tk::MainWindow->new;
my $topleft  = $mw->Pane(qw'-bg pink'   )->grid(qw/ -column 0 -row 0 /
+);
my $topright = $mw->Pane(qw'-bg purple' )->grid(qw/ -column 1 -row 0 /
+);
my $botleft  = $mw->Pane(qw'-bg green'  )->grid(qw/ -column 0 -row 1 /
+);
my $botright = $mw->Pane(qw'-bg orange' )->grid(qw/ -column 1 -row 1 /
+);
$mw->MainLoop;
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