Is byte 0xFF valid in a UTF-8 encoded string?

Can an UTF-8 string contain the byte开发者_开发百科 0xFF (255)?

No. It is specifically forbidden by the spec.

UTF-8, Number of 1 bytes,First code point is U+0000, Last code point is U+007F.
The bytes 0xFE and 0xFF do not valid in UTF-8.
The first byte is 0 in The UTF-8 when bytes only one.
[click image for more info about UTF-8 bytes]