draft-liman-tld-names-00.txt and bidi

Vint Cerf vint at google.com
Sun Mar 8 17:07:54 CET 2009

well, we have already made a rule that labels cannot have leading or  
trailing hyphens...

others more expert in the punycode algorithm will have to say whether  
it is possible for it to produce a terminating digit. One would think  
so given that digits are an allowed value among the A-Z, 0-9 and "-"  
components of LDH-label subset of ASCII labels.

Vint Cerf
1818 Library Street, Suite 400
Reston, VA 20190
vint at google.com

On Mar 8, 2009, at 11:53 AM, Andrew Sullivan wrote:

> On Sat, Mar 07, 2009 at 03:43:02PM +0900, Martin Duerst wrote:
>> You are right that there is a bidi issue. For some very specific
>> example, please see Example 11 at
>> http://www.w3.org/International/iri-edit/BidiExamples
>> (please read the legends or tooltips carefully).
>> The reason why there are bidi issues is:
>> - Non-IDN labels turn up in IDNs
>> - Digits get close to RTL characters, maybe only separated by dots
>> - In the bidi algorithm, numbers and dots get associated with nearby
>>  text and thrown around
> Ok.  Now the important question is, is it ever possible for Punycode
> to produce output that ends in a digit?  I haven't run into an example
> yet, but I haven't been able to convince myself that's anything but an
> accident.  If someone who understands the algorithm better than I
> says, "No, it can't, and here's why," then we'll be in a position to
> add to draft-liman-tld-names a restriction that a TLD must both begin
> _and end_ with an ASCII letter, and the problem will automatically go
> away.  Otherwise, we can't make that rule.  Right?
> A
> -- 
> Andrew Sullivan
> ajs at shinkuro.com
> Shinkuro, Inc.
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