UTF-9 is a Unicode character encoding introduced by the standards document RFC 4042 in 2005. UTF-9 and its sibling UTF-18 allow for efficient coding of Unicode characters on machines based on 36-bit words, using 9 and 18 bits per code point, respectively. Although they are completely valid in a technical sense, they are largely humorous, as virtually all computers designed after the early-mid 1980s use word sizes of powers of two, making these encodings largely obsolete.
- RFC 4042
- Wikipedia:April Fools' Day Request for Comments#2005: Very short Wikipedia entry on RFC 4042