my $mw = MainWindow->new();
...
build_main_pane(\$mw);
...
sub build_main_pane {
    my $mw = ${+shift};

    my $mp = $mw->Scrolled(q{Pane},
        -scrollbars => q{osoe},
        -sticky => q{nsew},
    );

    $mp->pack(-fill => q{both}, -expand => 1);

    build_notebook($mp);

    return;
}

sub build_notebook {
    my ($parent) = @_;

    my $nb = $parent->NoteBook();

    $nb->pack(-fill => q{both}, -expand => 1);

    build_pages($nb);

    return;
}

sub build_pages {
    my ($nb) = @_;

    build_example_page($nb);
    build_other_page($nb);
    ...
    build_last_page($nb);

    return;
}

sub build_example_page {
    my ($nb) = @_;

    my $example_page = $nb->add(example_page =>
        -label => 'Example Page',
        ...
    );

    ...
}