Next, there is the list of authorised users, introduced by a ‘^Au’ line. Only users in the authorised users list can modify the sccs file. This list always appears (though many implementations will not complain if you remove it with an editor) but is often empty. One user login name appears on each line. Lines can alternatively contain numbers, denoting whole groups of users (as listed in /etc/group on many systems). The authorised-users list is terminated with a ‘^AU’ line. Some broken implementations emit lines of the form ‘^AU 0’ here instead; the polite thing to do is to ignore gaffes of this sort. This is of course what CSSC does.