A well-formed Unicode code unit sequence of UTF-8 code units.

• The UTF-8 code unit sequence <41 C3 B1 42> is well-formed, because it can be partitioned into subsequences, all of which match the specification for UTF-8 in Table 3-7. It consists of the following minimal well-formed code unit subsequences: <41>, , and <42>.
• The UTF-8 code unit sequence <41 C2 C3 B1 42> is ill-formed, because it contains one ill-formed subsequence. There is no subsequence for the C2 byte which matches the specification for UTF-8 in Table 3-7. The code unit sequence is partitioned into one minimal well-formed code unit subsequence, <41>, followed by one ill-formed code unit subsequence, , followed by two minimal well-formed code unit subsequences, and <42>.
• In isolation, the UTF-8 code unit sequence would be ill-formed, but in the context of the UTF-8 code unit sequence <41 C2 C3 B1 42>, does not constitute an ill-formed code unit subsequence, because the C3 byte is actually the first byte of the minimal well-formed UTF-8 code unit subsequence . Ill-formed code unit subsequences do not overlap with minimal well-formed code unit subsequences.