Could someone possibly explain this to me in simpler terms or maybe provide an example? 
I'd like to block any special characters except -, _ and spaces
"username_invalid_chars: A list (may contain ranges using a dash) or characters (In hexidecimal notation using \xXX where XX is the hexidecimal number) which are not allowed in usernames. If you wish to disallow usernames with -'s in them, you must put the - at the end."
Realiiity.com Forums
I'd like to block any special characters except -, _ and spaces "username_invalid_chars: A list (may contain ranges using a dash) or characters (In hexidecimal notation using \xXX where XX is the hexidecimal number) which are not allowed in usernames. If you wish to disallow usernames with -'s in them, you must put the - at the end."
Realiiity.com Forums