OP (and the article) is talking about the encoding of UTF-8, not Unicode in general. ASCII is itself valid utf-8, because ASCII is a subset of utf-8. But a mul

OP (and the article) is talking about the encoding of UTF-8, not Unicode in general. ASCII is itself valid utf-8, because ASCII is a subset of utf-8. But a multi byte encoded codepoint in UTF-8 cannot be confused with ASCII, because the highest bit is set in all the octets.