Joomla!'s access control mechanisms are not as clear-cut as they could be; this is due to an ongoing development cycle that is moving away from a legacy access control system. In the future, Joomla! will use a complete GACL (Group Access Control Lists) access control mechanism.
The current access control mechanism uses an incomplete, abstracted implementation of
phpGACL. There are eleven user groups, sometimes referred to as
usertypes. Joomla! also maintains a set of three legacy access groups, Public, Registered, and Special.
The legacy groups are stored in the
#__groups table; theoretically this makes the legacy access groups dynamic. There is no mechanism for administrators to amend the legacy access groups and even if we manually ...