Mac OS X 10.4 Tiger
Access control lists (ACLs) implement more flexible file access permissions than the traditional POSIX scheme. To manage these ACLs, the chmod command has got a few new command-line options including +a -a =a -N, see the corresponding man page. I like most the -N option which actually removes an ACL from a file, for example
removes all ACLs recursively from the entire contents of the current directory.
Extended file attributes store additional file metadata like file type and creator. To manage these, the xattr command can be used, see the corresponding man page. For example
removes all extended attributes recursively from the entire contents of the current directory.
(I don’t like ACLs and extended attributes, POSIX permissions and the file command usually are sufficient.)