Re: Need for Level Direction Mark

From: Philippe Verdy <>
Date: Wed, 14 Sep 2011 11:12:33 +0200

2011/9/14 Richard Wordingham <>:
> On Wed, 14 Sep 2011 03:31:14 +0200
> Philippe Verdy <> wrote:
>> In other words, the UTC policy about the stability of Bidi classes
>> should be minimally relaxed, by rewording into something like:
>>     « The bidi class property value of any assigned code point is
>> IMMUTABLE (and will never change for the same assigned code point in
>> any subsequent versions of the UCS). »
> No.  At most it should become immutable after being unchanged for, say,
> 20 years.  It is unwise to prohibit correction.

Not needed. Even if there's an error, to avoid breaking usages, it
will be much better to reencode the character with a new Bidi class,
and not break the many texts already containing the character (notably
here because we're discussing about characters that are extremely
widely used, such as generic punctuations).

Corrections should be made in the early stages of beta releases, or
based on documents that lead to the initial encoding approval for
encoding. This should come only as erratas coming extremely fast (one
or two months?), and caused only by discovered editorial problems
which contradict the prior decision.

After 20 years, as you suggest, the cost for correcting the encoded
documents would be excessive, and the correction will not be applied
consistantly before about the same time or more. This would mean at
least about 30 years of unstability, and lots of data losses in that
period (which will be extremely hard to estimate in time and total
cost supported by all users of the UCS).

-- Philippe.
Received on Wed Sep 14 2011 - 04:15:32 CDT

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