idna-mapping update

John C Klensin klensin at
Wed Dec 23 15:01:03 CET 2009

--On Wednesday, December 23, 2009 11:35 +0000 Gervase Markham
<gerv at> wrote:

> On 22/12/09 19:17, John C Klensin wrote:
>> While I agree that looking at [standardized] keyboards could
>> be very useful, I see the way you stated the question as
>> interesting.  The odds that a standardized keyboard would have
>> the "fi" ligature as a letter key when people intended the
>> letter "f" and "i" to be represented is actually pretty low --
> Indeed. I picked it as an example in the hope that people
> wouldn't get distracted by the specifics of the example I
> picked :-)

I understood that.  But the issue generalizes.

> But how often did those whole words contain letters your
> keyboard was otherwise unable to type? If they didn't, then
> this fact (AFAICS) doesn't have any bearing on the question.

Hmm.  I read your example a slightly different way.  Coming back
to the "fi" example, I was assuming that "f" and "i" would be
available on the keyboard (as, e.g., "s" and "z" are) and the
presence of the ligature would be in addition.  If the ligature
where there and the individual characters that composed it were
not, one would have a rather different situation... and an
extremely powerful argument, not for mapping in IDNA but for
either an "fi" character in Unicode that did not have a
compatibility mapping to other characters or for a combining
(right-attaching) "i"-like character, the latter because "f"
plus "i" is two characters not something that forms a ligature
sequence (except possibly by rendering rules that tend to be
language or other context-specific and that don't help with
comparisons, especially in the no-available-context DNS


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