Using priority to control access

The Content Access README.txt says:

However you can influence the behaviour by changing the priority of the content access module as drupal applies *only* the grants with the highest priority. So if content access has the highest priority *alone*, only its grants will be applied.

I use two access control modules (as well as ACL). Content Access is one, the other is named ACL If and is written by me. I want to use priority to determine which module is used. Priority is 0 for Content Access (the default), and is 99 for ACL If.

The general idea is to use role based access to grant all authenticated users access, except when I assign an ACL to a node. In that case, I want the role based access rules from Content Access of to be ignored, and make access only decided by the highest priority ACL for the node.

I've created a ACL for node 2, and created an ACL for that node with priority 99 that only grants user john access.

This is how devel reports node access:

node	realm			gid	view	update	delete	explained
Node 2	acl			4	1	0	0	aclif/view_2: john
Node 2	content_access_rid	2	1	0	0	Content access: authenticated user can access

If I try to access this node, any authenticated user (i.e. not only john) can access. However, since 99 indicate a higher priority than zero, this is not what I expect.

My question is this: What do I need to do to have only the grants with the highest priority applied?

Or: Have I misunderstood the documentation in the Content Access README.txt?