You're doing the right things. I suggest you pull main out into a separate file - This has caused me grief in the past when writing classes involving inheritance.

This works perfectly for me:

#!/usr/bin/perl

use warnings;
use strict;

package MyPackage;
use parent 'SVG';

sub Foo {
    my ($self, $fooArg) = @_;
    return $self->rectangle(id => $fooArg, x => 10, y => 10);
}

sub Bar {
    my ($self, $barArg) = @_;
    my $g = $self->group(id => $barArg);
    return $g->Foo("g$barArg");
}

1;
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EDIT: Actually, looking a bit closer, you're doing $g = $self->group... This is returning a SVG::Element object, which of course you cannot call Foo on, as Foo is a function of MyPackage