> How would you index into or split an invalid UTF-8 string? Indexing/splitting by bytes is usually more useful than by Unicode code points anyways. Often, you

> How would you index into or split an invalid UTF-8 string? Indexing/splitting by bytes is usually more useful than by Unicode code points anyways. Often, you would want to split by a substring; if so, then it works just as well if you are treating them as sequences of bytes instead of code points; due to the self-delimiting feature of UTF-8, such a thing would work correctly (unlike e.g. Shift-JIS, which doesn't work correctly). Treating them as bytes when splitting by substrings also avoids needing to count the code points every time. > How would you apply a regex? You can apply byte-oriented regular expressions. (Often you will not need Unicode-oriented regular expressions, and you can still match UTF-8 strings with byte-oriented regular expressions.) > What is its length? It depends on why you want to measure it. Usually, the number of bytes is the most useful kind of measurement, is what it seems to me. > How do you deal with other systems that do validate UTF-8 strings? It depends. Sometimes it is better to just not deal with such systems (or to fix them if you can). Sometimes you might treat the input as ISO-8859-1 and convert it to UTF-8, or as bytes and convert it to base64, just so that the other system won't complain. In a few cases, doing the validation would be appropriate, though. > scanning a sequence of byte for invalid UTF-8 sequences is validating. ... It's probably also a lot slower as you have to always do this for every operation, whereas once you've validated a string you can operate on it with impunity. Usually you should not need to do this scanning at all; just use the bytes as they are. Of course, you can add the validation step once where needed if you really do need this validation, but usually you shouldn't need it. It is also notable that you cannot always assume strings are Unicode anyways; there are problems with Unicode anyways and you might have strings with other character sets (or none at all).