Unicode Demystified

UTF-7

You might run across some other, less common, Unicode transformation formats. The most common of these formats is UTF-7, which was designed for use in 7-bit ASCII environments that can't handle 8-bit characters. In particular, the original version of the Simple Mail Transfer Protocol (SMTP), which is still in common use, wouldn't work with 8-bit character values and required this approach.

UTF-7 works by using a scheme similar to the numeric-character reference scheme employed in HTML and XML. Most of the ASCII characters are just themselves, but a few are used to signal sequences of characters that specify otherwise unrepresentable Unicode values. Thus, unlike the other Unicode transformation formats, UTF-7 is a stateful encoding, with ...