Re: SCSU/BOCU-1 Compressibility of the Yi syllabary

From: Doug Ewell (
Date: Sun Jul 17 2005 - 13:55:14 CDT

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    Richard Wordingham <richard dot wordingham at ntlworld dot com> wrote:

    > 2. Of the codes used with the SDn and UDn tags, "A8..F8 [are]
    > reserved for future use".
    > Perhaps this future is approaching. As single-byte mode does compress
    > the Yi syllabary, it seems reasonable to suggest using:
    > Codes A8..B7 for Half-blocks with starts from U+A400 to U+AB80
    > Code B8 for Half-block starting D780. (The road map shows unused
    > space here.)
    > The biggest objection will, of course, be that existing SCSU decoders
    > will not recognise these codes. The SCSU is not something to be
    > updated frequently - which means any changes may have to be *big*.

    Good to hear from someone else who has spent a lot of time thinking
    about SCSU.

    In discussions with some UTC members while I was finishing UTN #14, it
    became apparent that there is strong resistance to the idea of expanding
    SCSU by assigning the unused window-offset values, even though they are
    marked "reserved for future use," or by making other such changes. The
    concern, as you said, is that existing decoders would reject the encoded
    text, and that creating a "SCSU version 2" would fragment the
    already-small user base for SCSU and discourage its use.

    I happen to believe in a lot of what you are saying, but I can see both
    sides of this.

    Perhaps these ideas could be structured into a more-or-less formal UTC

    BTW, my specific proposal was to remove the "reserved for future use"
    status from the single-byte value 0x0C, if it is not going to be used
    for any new tag type. This would allow ASCII or Latin-1 text that
    contains form feeds to be valid SCSU. I can see how this change by
    itself might not be "big" enough to justify an update, as you mentioned.

    Doug Ewell
    Fullerton, California

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