What Unicode characters are dangerous?

Question

What Unicode characters (more precisely codepoints) are dangerous and should be blacklisted and prohibited for the users to use? I know that BIDI override characters and the "zero width space" are very prone to make problems, but what others are there?

Thanks

Answer 1

Characters aren’t dangerous: only inappropriate uses of them are.

You might consider reading things like:

• Unicode Standard Annex #31: Unicode Identifier and Pattern Syntax
• RFC 3454: Preparation of Internationalized Strings (“stringprep”)

It is impossible to guess what you mean by dangerous.