Unicode::UTF8 now allows noncharacters; they receive no special handling and are processed like any other code point.
According to Corrigendum #9, noncharacters (the values U+nFFFE and U+nFFFF (where n is from 0 to 10^16) and the values U+FDD0..U+FDEF) are permanently reserved but should be allowed in interchange. <https://www.unicode.org/versions/corrigendum9.html>