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Re: [precis] Review of current document draft-ietf-precis-framework-20

Patrik Fältström <paf@frobbit.se> Mon, 08 December 2014 05:58 UTC

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From: Patrik Fältström <paf@frobbit.se>
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Date: Mon, 08 Dec 2014 06:58:03 +0100
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To: Peter Saint-Andre - &yet <peter@andyet.net>
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Subject: Re: [precis] Review of current document draft-ietf-precis-framework-20
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> On 8 dec 2014, at 04:49, Peter Saint-Andre - &yet <peter@andyet.net> wrote:
> 
>> I would recommend explicitly mentioning the fact (destructive)
>> transformation might occur in this step.
> 
> Destructive transformation doesn't sound good. Do you have examples of what that means?

When you do a transformation that does not have an inverse. For example lowercase.

uppercase(lowercase(cp)) is not cp for all values of cp.

In IDNA2003, the mappings where destructive, which implied that "toascii(unicode string)" (within quotes, because I think you know what I talk about) is not possible to reserve.

In IDNA2008, the ascii version and unicode version of a domain name are 1:1 mappings and the transformation can be done however many times you want.

This because the mapping is _removed_ from IDNA2008, so IF one is interested in doing mappings, that is to be done before IDNA2008 is applied. Anything "inside" IDNA2008 consists of strings either in their ASCII version (xn-- thing) or Unicode version (in Unicode). And it is possible to transform one to the other back and forth.

   Patrik

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