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.
These codepoints currently are not successfully encoded or decoded - by default, they are replaced by replacement characters (at least for UTF-8).
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.
These codepoints currently are not successfully encoded or decoded - by default, they are replaced by replacement characters (at least for UTF-8).