Anyone can extend UTF-16 to the UTF-8 repertoire of codepoints by using the top 2 private use planes as high and low 2nd-tier surrogates respectively. Hopefully

Anyone can extend UTF-16 to the UTF-8 repertoire of codepoints by using the top 2 private use planes as high and low 2nd-tier surrogates respectively. Hopefully, by the time UTF-8 (and UTF-32) need to be extended, UTF-16 will have fallen into general disuse and almost no-one will need to use those 2 levels of surrogates. Java/Android and .NET strings aren't being broken anytime soon, however, so it seems to me people should start talking about the details of such a 2nd-tier surrogate system.