Bidi tests on labels or domains?

Simon Josefsson simon at josefsson.org
Sun Jan 9 16:24:33 CET 2011


Vint Cerf <vint at google.com> writes:

> Simon,
>
> all of the tests in IDNA2008 are oriented around labels, not around domain
> names. This means that each test applies, independently, to each label. The
> existence of an RTL label does not necessarily force any special testing on
> other labels in the domain name. If any particular label contains an RTL
> character (ie is take from an RTL-script), that label needs to be bidi
> tested.
>
> the clue is here:
>
> If the proposed label contains any characters from scripts that are
>   written from right to left, it MUST meet the Bidi criteria [RFC5893].
>
> since these are label by label tests (and not inter-label tests), only those
> labels that actually contain RTL characters need to be tested.

Thank you for clarification (again!) -- this is good as it simplifies
implementation somewhat.

/Simon

> vint
>
>
>
> On Sun, Jan 9, 2011 at 5:50 AM, Simon Josefsson <simon at josefsson.org> wrote:
>
>> Hi,
>>
>> I need help with interpretation of this text in RFC 5891:
>>
>> 4.2.3.4.  Labels Containing Characters Written Right to Left
>>
>>   If the proposed label contains any characters from scripts that are
>>   written from right to left, it MUST meet the Bidi criteria [RFC5893].
>>
>> The terminology used in RFC 5893 suggests to me that _all_ labels, not
>> just a RTL-label, in a bidi domain name needs to be tested:
>>
>>   Section 2 defines a rule, the "Bidi rule", which can be used on a
>>   domain name label to check how safe it is to use in a domain name of
>>   possibly mixed directionality.
>> ...
>>   A "Bidi domain name" is a domain name that contains at least one RTL
>>   label.
>> ...
>>   "RTL" and "LTR" are abbreviations for "right to left" and "left to
>>   right", respectively.
>> ...
>>   An RTL label is a label that contains at least one character of type
>>   R, AL, or AN.
>> ...
>>   The following rule, consisting of six conditions, applies to labels
>>   in Bidi domain names.
>>
>> I can't resolve my different readings.  To my questions:
>>
>> 1) Is the bidi rule in 4.2.3.4 intended to be invoked on a non-RTL label
>>   if the domain name under testing is a bidi domain name?
>>
>> 2) Is the same approach intended in section 5.4?  It currently reads:
>>
>>   o  Verification that the string is compliant with the requirements
>>      for right-to-left characters specified in the Bidi document
>>      [RFC5893].
>>
>>   The term "string" is used to refer both to labels and domains in
>>   section 5, causing my confusion.
>>
>> /Simon
>> _______________________________________________
>> Idna-update mailing list
>> Idna-update at alvestrand.no
>> http://www.alvestrand.no/mailman/listinfo/idna-update
>>
> _______________________________________________
> Idna-update mailing list
> Idna-update at alvestrand.no
> http://www.alvestrand.no/mailman/listinfo/idna-update


More information about the Idna-update mailing list