NSM flaw?

Vint Cerf vint at google.com
Mon Sep 14 15:55:35 CEST 2009

Martin, Abdulrahman,

thanks for this contribution. I think Martin's points are very well  
Finding protocol level rules for situations like that is not only very
hard but probably not productive because of all the various potential
hazards that exist with the introduction of so many new scripts.
The programs implementing very complex rules increases the
risk of bugs in the programs and thus, incompatibilities in
implementation. The observation about varying treatment at
browser level underscores some of the hazards.


On Sep 14, 2009, at 7:16 AM, Martin J. Dürst wrote:

> Hello Abdulrahman,
> Are you saying that there is a problem with two successive (identical)
> vowel marks (such as fatha, damma, kasra) because display engines will
> ignore the second one (because essentially, there is no point in
> indicating the vowel twice)?
> First, my mail agent (Thunderbird) displays both U+064E characters in
> your examples below (the second one above a (maybe dotted, but I can't
> see the actual dots) circle. But there may well be display engines  
> that
> do what I think you say, so this may indeed be a problem.
> Second, while such NSM combinations (as well as much more far-fetched
> combinations of NSMs, or letters and NSMs, or letters and letters) are
> all allowed in the protocol, registries can (and in the case you point
> out most probably should) reject them. Because of the complexity of
> languages and scripts around the world, it wasn't possible to
> incorporate such restrictions (except for a few extremely crucial  
> ones)
> into the protocol, but it would definitely be good if the cases you
> point out are documented by the group working on Arabic domain  
> names. I
> have cc'ed the Arabic Scripts IDNA mailing list, maybe they are  
> already
> aware of this and related issues.
> Regards,   Martin.
> On 2009/09/14 19:21, Abdulrahman I. ALGhadir wrote:
>> Hello,
>> I am Abdulrahman I. Al-Ghadir from SaudiNIC. I am new to IDNA and  
>> joined the mailing list lately.
>> While revision and reading the last drafts I found something which  
>> may be a flow in the protocol in draft ftp://ftp.ietf.org/internet-drafts/draft-ietf-idnabis-bidi-05.txt 
>>  ,
>> In bidi-05 “2.  The BIDI Rule”:
>> “  2.  In an RTL label, only characters with the BIDI properties  
>> R, AL,
>>        AN, EN, ES, CS, ET, ON, BN and NSM are allowed.
>>    3.  In an RTL label, the end of the label must be a character with
>>        BIDI property R, AL, EN or AN, followed by zero or more
>>        characters with BIDI property NSM.”
>> A sequence of NSM can be represented in the label thus this may  
>> arise a problem on the display level for the label.
>> Assume these two labels (image attached for both words):
>> سيارةَ          ->            u0633\u064A 
>> \u0627\u0631\u0629\u064E                     ->    xn--mgbexg9i1a
>> سيارةََ          ->            u0633\u064A 
>> \u0627\u0631\u0629\u064E\u064E       ->   xn--mgbexg9i1aa
>> http://unicode.org/cldr/utility/idna.jsp?a=%D8%B3%D9%8A%D8%A7%D8%B1%D8%A9%D9%8E%0D%0A%D8%B3%D9%8A%D8%A7%D8%B1%D8%A9%D9%8E%D9%8E&f= 
>> [%C3%9F+%CF%82+[%3AJoin_C%3A<http://unicode.org/cldr/utility/idna.jsp?a=%D8%B3%D9%8A%D8%A7%D8%B1%D8%A9%D9%8E%0D%0A%D8%B3%D9%8A%D8%A7%D8%B1%D8%A9%D9%8E%D9%8E&f=%5b%C3%9F+%CF%82+%5b%3AJoin_C%3A 
>> >
>> As you see both words have same display but different codes which  
>> might leads to problems same goes with other because as you know  
>> NSM display is the same position and rest of NSM which are after it  
>> will be display on same position too(later NSM after first NSM  
>> displayed will be invisible), same goes to other NSMs which act in  
>> same behavior. (am I right?)
>> I know it is abit late to arise  things like that but it may be a  
>> problem?
>> Thank you,
>> Abdulrahman.
>> -----------------------------------------------------------------------
>> تنويه:
>> هذه الرسالة و مرفقاتها (إن وجدت) تمثل  
>> وثيقة سرية قد تحتوي على معلومات تتمتع  
>> بحماية وحصانة قانونية. إذا لم تكن  
>> الشخص المعني بهذه الرسالة يجب عليك  
>> تنبيه المُرسل
>> بخطأ وصولها إليك، و حذف الرسالة و  
>> مرفقاتها (إن وجدت) من الحاسب الآلي  
>> الخاص بك. ولا يجوز لك نسخ هذه الرسالة  
>> أو مرفقاتها (إن وجدت) أو أي جزئ منها،  
>> أو
>> البوح بمحتوياتها لأي شخص أو  
>> استعمالها لأي غرض. علماً بأن الإفادات  
>> و الآراء التي تحويها هذه الرسالة تعبر  
>> فقط عن رأي المُرسل و ليس بالضرورة رأي  
>> هيئة الاتصالات و
>> تقنية المعلومات، ولا تتحمل الهيئة أي  
>> مسئولية عن الأضرار الناتجة عن هذ  
>> البريد.
>> ------------------------------------------------------------------------
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> -- 
> #-# Martin J. Dürst, Professor, Aoyama Gakuin University
> #-# http://www.sw.it.aoyama.ac.jp   mailto:duerst at it.aoyama.ac.jp
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