Virtgroup class generates special kinds of group objects whose children can be a lot larger than the actual group. The group acts as a (small) window through which a rectangle area of its contents is visible.
Layout of a virtual groups children doesn't depend on the space available for the virtual group object. The children will get as much room as they want, usually their default size.
Virtual groups themselves don't offer any scrollbars to allow user interaction. These things are handled by scrollgroup class.