draft-klensin-idnabis-protocol-04 section 4.5

Martin Duerst duerst at it.aoyama.ac.jp
Fri Mar 28 07:46:44 CET 2008

This is irrelevant to the charter, but I have difficulties understanding
from the citations below how registration is stricter than lookup.
Registration only mentions DISALLOWED and UNASSIGNED, whereas
lookup mentions NFC, contextual rules, and combining marks in
first position on top of that. So I get the impression that
lookup is more restricted that registration. What did I get wrong?

Regards,   Martin.

At 21:37 08/03/27, Harald Alvestrand wrote:

> From draft-klensin-idnabis-protocol-04:
>4.3.  Permitted Character and Label Validation
>4.3.1.  Rejection of Characters that are not Permitted
>   The Unicode string is examined to prohibit characters that IDNA does
>   not permit in input.  Those characters are identified in the
>   "DISALLOWED" and "UNASSIGNED" lists that are discussed in
>   [IDNA200X-Rationale].  The normative rules for producing that list
>   and the initial version of it are specified in [IDNA200X-Tables].
>   Characters that are either DISALLOWED or UNASSIGNED MUST NOT be part
>   of labels being processed for registration in the DNS.
>5.4.  Validation and Character List Testing
>   In parallel with the registration procedure, the Unicode string is
>   checked to verify that all characters that appear in it are valid for
>   IDNA resolution input.  As discussed in [IDNA200X-Rationale], the
>   resolution check is more liberal than that of the registration one.
>   Putative labels with any of the following characteristics MUST BE
>   rejected prior to DNS lookup:
>   o  Labels containing code points that are unassigned in the version
>      of Unicode being used by the application, i.e., in the
>      "Unassigned" Unicode category or the UNASSIGNED category of
>      [IDNA200X-Tables].
>   o  Labels that are not in NFC form.
>   o  Labels containing prohibited code points, i.e., those that are
>      assigned to the "DISALLOWED" category in the permitted character
>      table [IDNA200X-Tables].
>   o  Labels containing code points that are shown in the permitted
>      character table as requiring a contextual rule and that are
>      flagged as requiring exceptional special processing on lookup
>      ("CONTEXTJ" in the Tables) MUST conform to the rule, which MUST be
>      present.
>   o  Labels containing other code points that are shown in the
>      permitted character table as requiring a contextual rule
>      ("CONTEXTO" in the tables), but for which no such rule appears in
>      the table of rules.  With the exception in the rule immediately
>      above, applications resolving DNS names or carrying out equivalent
>      operations are not required to test contextual rules, only to
>      verify that a rule exists.
>   o  Labels whose first character is a combining mark. [[anchor15: Note
>      in Draft: this definition may need to be further tightened.]]
>.... more text follows .....
>> What I'm trying to understand is what an IDNA200x implementation will do
>> (i.e., which output string or what error) when the user types 'josef゜on'
>> or 'dェtェkonsult'.
>Read the drafts. It helps.
>                 Harald
>Idna-update mailing list
>Idna-update at alvestrand.no

#-#-#  Martin J. Du"rst, Assoc. Professor, Aoyama Gakuin University
#-#-#  http://www.sw.it.aoyama.ac.jp       mailto:duerst at it.aoyama.ac.jp     

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