Well, we try to use explicit name like sale group is to have access to sale orders, account for accounting etc. And the group ended by “Administration” is to have access to setup.
For more detail, you have to look at the “Access Permission” tab of the group.
The is no hierarchy, the group implementation is flat.
Such documentation that repeat the XML configuration tent to become inaccurate very quickly. We prefer that the application is self documented (especially because of its modular nature).