XF 1.5 Prevent All CAPS in Usernames


I know this has been asked before, and I found a thread that had some examples of how to do this. But I have no clue what any of this stuff means. It might as well be in Chinese.

I just want to be able to prevent new registrations using all CAPS in their username. That's it. Numbers are fine. Spaces are fine. A capital letter in their first and last name is fine. I just don't want ALL CAPS. This is what I currently have, and since I implemented this, 2 people have signed up with all CAPS in their usernames,lol.