From: Doug Ewell (firstname.lastname@example.org)
Date: Thu Feb 08 2007 - 08:35:41 CST
Markus Scherer <markus dot icu at gmail dot com> wrote:
>> I'm sure it is arbitrary, in the sense that every "exceptional" large
>> block adds some complexity to the algorithm,
> Yes and no. Yes, it's arbitrary - when you design a charset or a data
> structure, you design and optimize it for what you deem important or
Absolutely correct. "Arbitrary" does not mean "capricious" here.
>> I think the goal was to ensure that the entire block was accessible
>> via 2-byte sequences.
> This is the key: Without special handling for Unihan and Hangul, it
> would use 3-byte sequences for many of the characters. This is not a
> problem for Yi and other "large" blocks that have fewer than 10000
> code points because they always stay within the range of 2-byte
I hadn't done the math, but of course you are right. It might be a good
idea to add this point somewhere in the BOCU-1 spec (UTN or UTS).
> In general, if you make an incompatible change - a change where an old
> decoder cannot cope with the output from an updated encoder - then you
> must change the name of the charset.
UTF-8 was initially defined to work across the entire original 31-bit
ISO 10646 code space, with sequences up to 6 bytes long, before Unicode
and 10646 agreed to limit the range to U+10FFFF. The definition of
UTF-8 appears to have been changed, and I've personally seen several
decoders that recognized the longer sequences, but AFAIK the name
"UTF-8" was never changed or qualified with a version number.
I do wonder, as I did months ago when we had this discussion, how many
SCSU decoders have been written that recognize a bare 0C as an error. I
realize this is a pragmatic view and not a pure one. I did write my
decoder to flag unquoted 0C as an error, but I could have chosen to
accept it since Section 4 (conformance clause C1) says "The action of a
conformant decoder on illegal or reserved input is undefined."
-- Doug Ewell * Fullerton, California, USA * RFC 4645 * UTN #14 http://users.adelphia.net/~dewell/ http://www1.ietf.org/html.charters/ltru-charter.html http://www.alvestrand.no/mailman/listinfo/ietf-languages
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