The next code will prove to add the groups selector widget towards the WordPress Page editor interface...

add_action('admin_menu', 'my_post_categories_meta_box');
function my_post_categories_meta_box() {
    add_meta_box('categorydiv', __('Categories'), 'post_categories_meta_box', 'page', 'side', 'core');
}

What I must do would be to learn how to customize the resulting category listing to ensure that it only consists of a predefined listing of hard coded groups which i define.

Since I am adding this via my custom theme, it'll only show up on the page editor when my theme is active on the website. And That I possess some specific "handler" groups that my theme installs in to the site and then uses to find out layout elements. I only want these groups to become listed during this demonstration of the groups widget.