CORRESPONDENCE BETWEEN ACL ENTRIES AND FILE PERMISSION BITS
     The permissions defined by ACLs are a superset of the permissions speci-
     fied by the file permission bits.

     There is a correspondence between the file owner, group, and other per-
     missions and specific ACL entries: the owner permissions correspond to
     the permissions of the ACL_USER_OBJ entry. If the ACL has an ACL_MASK
     entry, the group permissions correspond to the permissions of the
     ACL_MASK entry.  Otherwise, if the ACL has no ACL_MASK entry, the group
     permissions correspond to the permissions of the ACL_GROUP_OBJ entry.
     The other permissions correspond to the permissions of the ACL_OTHER_OBJ
     entry.

     The file owner, group, and other permissions always match the permissions
     of the corresponding ACL entry. Modification of the file permission bits
     results in the modification of the associated ACL entries, and modifica-
     tion of these ACL entries results in the modification of the file permis-
     sion bits.