The Yii User Management Module version 0.8 introduces a new Permission System. 

This document will describe the basics of the configuration and usage, since
it is neither a pure RBAC nor a ACL based system. It is relatively simple,
tough.

At first, we have the classical roles. A User can be in none, one or many
roles. 

Then, we have the permission. A Permission can be either granted to a specific
user or to a Role, in which case the permission is granted for every User
in the role. A Permission furthermore has a assigned action, that specifies,
to which action a user is allowed. 

For example, if we assign the user 'Bob' the permission to run a action
'removeUsers', we can check if Bob has the permission by:

if(YumUser::model()->find('username = bob')->can('removeUsers')) { ...

A Permission can also have a Subordinate. With this feature, you can 
further restrict, what a action can affect. 

A Membership system is also available. A membership acts as a temporary
role assignment to a user that expires after some time.
