[RESOLVED] Limiting input text to unique characters

[Rajada]

I already know how to limit my input text to a number of characters, but how would I go about (if possible) making sure characters do not repeat? In other words, I have a ten character input text box and I want you to be able to type pretty much any character but only one of each.

Example:

AFKEIOPCNK

What I'm trying to eliminate is this:

AANHDKDDJI

If that isn't possible, I'd like to instead detect if there are repeated characters so I can just say "that's invalid".