The Two Lookups Approach (was Re: Parsing the issuesand finding a middle ground -- another attempt)

Erik van der Poel erikv at
Sun Mar 8 05:44:37 CET 2009

On Sat, Mar 7, 2009 at 8:33 PM, John C Klensin <klensin at> wrote:
> --On Saturday, March 07, 2009 19:44 -0800 Erik van der Poel
> <erikv at> wrote:
>> Another aspect of this, which I am not sure you've captured in
>> your drafts, is the Unicode version in use in a particular
>> U-label. For example, in a protocol involving U-labels, it
>> might be good to specify what to do when a sender sends a
>> U-label containing characters from a newer version of Unicode
>> than the receiver has implemented.
> Almost by definition, the receiver can't tell whether what the
> sender has sent it valid in a newer version of Unicode or just
> an attempt to cause whatever problems using an unassigned code
> point causes.   If the receiver has enough information to know
> that the character is actually supported in a particular later
> version of Unicode, it would require a strange situation indeed
> for it to not support that character (and that version of
> Unicode).  So I'm not quite sure how one would identify the
> situation you describe, much less why it should need special
> terminology.

I'm not suggesting that it needs special terminology. I'm just saying
that something that might be a valid U-label according to a sender
might be invalid according to a receiver. "U-label" is in the eye of
the beholder. One says it is a U-label, the other says it isn't.

So I guess I strayed from the topic (terminology). It is still an
interoperability problem.


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