You can cause the script to barf by entering certain characters into the invalid username character field....

A fatal error has occurred:

Invalid [] range "/-+" before HERE mark in regex m/[\x00-\x1f?*`¬|\\~#'@:;><.,/-+ << HERE =^!]/

Please enable debugging in setup for more details.

I want to block these characters so it looks like they should be escaped properly first.