Bidi tests on labels or domains?

Simon Josefsson simon at
Sun Jan 9 11:50:49 CET 2011


I need help with interpretation of this text in RFC 5891:  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
   "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 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

   The term "string" is used to refer both to labels and domains in
   section 5, causing my confusion.


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