Nothing. If you accept only workable specific subset of Unicode and validate input, you can get the point back. Using utf-8 encoding for text is almost always

Nothing. If you accept only workable specific subset of Unicode and validate input, you can get the point back. Using utf-8 encoding for text is almost always the right ting to do, treating it as generic Unicode string is usually wrong. Unicode is as complex as UTF-8 encoding is simple an neat. Joel Spolsky studied Unicode and was so sure that he understood it that he wrote a short intro for programmers without knowing that code points in Unicode don't correspond to "platonic ideal letters" aka user perceived characters. They correspond only in every case he used them (user-perceived character may actually be a sequence of code points).