Restrict spaces and punctuation in community usernames

I would suggest adding the ability to restrict the use of spaces or special characters in community usernames.

We have a standard FirstL username convention that we enforce for community members, and if they enter a user name that is already in use, we ask that they enter a number at the end.  I am finding that may users are creating duplicate user names that we must update because they are adding spaces or punctuation (periods):  Example: JohnF, John F, John F., JohnF.  If we could restrict the use of spaces and punctuation, it would reduce the amount of time we spend updating usernames to ensure that each member has an unique user name.