"As RBAC can operate at a much more general level than ACL, it will often happen that one role embraces another. Suppose we think of the example of a hospital, the role of consultant might include the role of doctor. Not everyone who has the role of doctor would have the role of consultant. But all consultants are doctors.
"At present, Aliro implements hierarchy purely for backwards compatibility with the Mambo, and Joomla! schemes, where there is a strict hierarchy of roles for ACL. The ability to extend hierarchy more generally is feasible, given the Aliro implementation, and may be added at some point."
