But it is a great QA check on any text field, which should either cleanly reject it in some manner [1] XOR accept it and process it "correctly" for whatever that means locally, but not something in between.
[1]: A lot of Unicode processing nowadays puts in the Unicode replacement character for unknown characters, but for the ASCII control codes I'd say you've often got a solid security case to say "Someone's just trying to screw with the system, we'll just filter it out entirely" for them. Excepting the ones we still use, basically \r \n \t, there's not much reason to keep them. (Think twice about \v "vertical tab" and think three times about letting \b "backspace"s through. Inconsistent behaviors by various layers of code are scary.)
Thanks for the info!
Which is exactly why I'd be wary of such clever password schemes on any account I cared about.
At the very least try to use one of them (generally a simple alt-code works, the first smiley face is just alt+1), it's a pretty good indicator of which sites are mucking with your passwords.
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Edit: Turns out HN strips a bunch of them, so my smilies and a bunch of others didn't make the cut!