Re: The "prohibited" encodings...

From: Doug Ewell (
Date: Wed Dec 30 2009 - 21:15:00 CST

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    Andrew Lipscomb <ewwa at chattanooga dot net> wrote:

    > Except that UTF-32 *isn't* on the banned list that started this
    > thread--discouraged, though, as I understand it. The fourth one was
    > CESU-8 (which, granted, has only one character that can be encoded two
    > ways, the NULL).

    CESU-8 doesn't have any characters that can be encoded two ways. You
    may be thinking of a different encoding.

    CESU-8 is simply UTF-8 applied to UTF-16 code units instead of Unicode
    scalar values. A supplementary character like U+10000 is encoded as <ED
    A0 80 ED B0 80> instead of <F0 90 80 80>. (Note that UTR #26
    incorrectly quotes this as <ED AE 80 ED B0 80>, which is the CESU-8
    encoding for U+F0000, an earlier example.) All BMP characters,
    including U+0000 NULL, are encoded the same in both CESU-8 and UTF-8,
    which of course is the biggest problem with CESU-8.

    Doug Ewell  |  Thornton, Colorado, USA  |
    RFC 5645, 4645, UTN #14  |  ietf-languages @ ­

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