UR::Object::Viewer::Aspect - a base class for a viewer which renders a particular aspect of its subject

    $v = $obj->create_viewer(
        visible_aspects => [qw/some_property some_method/], 
    );
    $v->show_modal();

    $v->set_subject($another_obj_same_class);
    $v->show();
    App::UI->event_loop();