In traditional *nix ACLs if the user is the owner of the file it uses that permission and ignores the rest, if he's not it check the group owner to see if he's in that group and uses those permissions, if not it uses everyone. However with Posix ACL there's a lot more possible conflicts. I believe the owner is checked first, and then to see if they have a specific user ACL, if not it checks the groups, then everyone. However, I'm not sure how this works. If a user is in 2 groups who both have ACLs set and 1 offers read/execute and the other one just has write does he get read/write/execute or what? Does it stop at the first group it sees? What about the group owner permission? Does the owner take precendence over the user specific setting.