As a matter of policy, and a simple interface, should we allow set-file-mode to set anything other than the permission bits? If not, should we rename it to set-file-permission-bits and apply a mask to the input, or signal an error if anything beyond the permission bits is supplied? Does it make any sense to allow setting additional but not set-uid or set-gid bits here? I personally have never manually set the sticky bit on a directory....