[bloak]

RFC 2279 says: "In UTF-8, characters are encoded using sequences of 1 to 6 octets." That's not technically a standard, but it was widely implemented.

[mark-r]

UTF-8 was originally designed to handle codepoints up to a full 32 bits. It wasn't until later that the codepoint range was restricted so that 4 octets would be sufficient.