how to Filter usernames at registration

[kh99]

You could put a regular expression in the Username Regular Expression field of the User Registration Options. I think something like [a-zA-Z@\._ ] would require at least one of those characters to be in the user name, and so it couldn't be all numbers. (I haven't thought about this a whole lot so that might not be the ideal regexp to use. For instance, maybe you'd rather use [a-zA-z] to require at least one letter somewhere in the name to disallow things like 123_456.)