Bidi tests on labels or domains?

[Vint Cerf]

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.

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
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.alvestrand.no/pipermail/idna-update/attachments/20110109/fd076a0d/attachment.html>