Comment by skitter

Annoyingly, Java, JavaScript, Windows file paths and more don't quite use UTF-16 (well, even if they did, that would be annoying) — they allow unpaired surrogates, which don't represent any Unicode character. So if you want to represent e.g. an arbitrary Windows file path in UTF-8, you can't; you have to use WTF-8 (wobbly transformation format) instead.