referencing IDNA2008 (and IDNA2003?)

"Martin J. Dürst" duerst at
Sun Oct 24 04:36:11 CEST 2010

On 2010/10/23 5:18, John C Klensin wrote:

> You have to sniff a little bit.  The problem is that, if you
> apply "various IDNA algorithms to Y", the effective first step
> under IDNA2008 is to determine whether there are non-ASCII
> characters present.  If there are not, there is no IDNA
> algorithm to apply.  Now you could build a perfectly conforming
> IDNA2008 implementation that would behave pretty much like
> ToASCII does in that regard, i.e., return the plain-ASCII string
> if the input was plain ASCII, return the A-label if the string
> was a U-label, and return a failure indication otherwise.   But,
> as far as the Standard is concerned, you cannot apply IDNA2008
> conversion to an A-label to an all-ASCII string.

It looks like from the viewpoint of a protocol using IDNA, what is 
missing in IDNA2008 (don't know about IDNA2003) is that there is nothing 
for the 'usual' case where:
- You want to say that you have either an NR-LDH or an U-Label
- You want to say that you have either an NR-LDR or an A-Label
- You want to say that you covert U-Labels to A-Labels, but leave NR-LDH 
- You want to say that you covert A-Labels to U-Labels, but leave NR-LDH 

If and when we are going to update the IDNA2008 texts, I think we should 
carefully look at this.

Regards,   Martin.

#-# Martin J. Dürst, Professor, Aoyama Gakuin University
#-#   mailto:duerst at

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