[mdlug] SUID for a directory?

[Michael ORourke]

I was reading a text the other day and it suggested setting the following 
permissions on a directory as such:
chmod -R ug+rwxs,o-w,o+rx /path/to/some/dir
Which basically gives "drwsrwsr-x" to the directory.  Now I understand 
wanting to set the SGID bit for the directory, but I don't see what the SUID 
bit does for the directory.  I googled it and the answers I am getting say 
that the SUID bit is undefined for a directory.  Anyone have any better 
answers?  My other thought is the author just made a simple mistake when he 
wrote that command.

-Mike