I'm astonished too. The section on use cases doesn't help to justify why we need all this complexity. Maybe they are trying to compensate for the inefficiency of the Unix permission system ( having user, group and world is lacking in a lot of situations by today standards ).
The other solution is to implement a totally different mechanism ( ACL + some other thing, Capabilities ) but then you lose retrocompatibility.
The other solution is to implement a totally different mechanism ( ACL + some other thing, Capabilities ) but then you lose retrocompatibility.