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Bidi: is stringprep broken?

From: Roy Badami <roy@gnomon.org.uk>
Date: Sun, 7 Sep 2003 17:01:48 +0100
Message-ID: <16219.22124.496586.659963@moriarty.gnomon.org.uk>
To: ietf-imaa@imc.org, public-iri@w3.org

I wrote:

 >  > Ergo, we need another display model; this one doesn't work 
 > There are also other real nasties with this display model:

Worse than that, I think the bidi restrictions in stringprep don't
actually achieve their goal of ensuring that you can't have two
different labels that render the same.

Consider the labels:

	A-123,456B

and

	A456,-123B

Here, A is HEBREW LETTER ALEF, B is HEBREW LETTER BET (or any
characters of bidi class R that you like, but *not* arabic letters,
which are class AL) and the comma is actually ARABIC COMMA U+060C (or
any character of class CS or ES).

As far as I can tell these both pass nameprep with UseSTD13ASCIIRules
set, and they both render identically under bidi as:

	B-123,456A

If you don't care about UseSTD13ASCIIRules, you can replace
ARABIC COMMA with COMMA, SOLIDUS or COLON.

I fully expect someone to reply explaining why I'm mistaken, but I've
checked the above as best I can...

	-roy
Received on Sunday, 7 September 2003 12:02:10 GMT

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