Re: [Lucid] Please clarify the i's in Appendix A

Shawn Steele <Shawn.Steele@microsoft.com> Sat, 21 March 2015 19:40 UTC

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From: Shawn Steele <Shawn.Steele@microsoft.com>
To: Andrew Sullivan <ajs@anvilwalrusden.com>, "lucid@ietf.org" <lucid@ietf.org>
Thread-Topic: [Lucid] Please clarify the i's in Appendix A
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Date: Sat, 21 Mar 2015 19:40:23 +0000
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Subject: Re: [Lucid] Please clarify the i's in Appendix A
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> What you're saying, actually, is that "most implementations" do casefolding of upper-case input strings prior to IDNA processing according to an approach that Unicode has (in this case pre-?) published?  I'm just trying to understand.

In IDNA 2008 it was recognized that mappings existed in IDNA2003 and that implementations such as browser address bars would find them useful.  It was also recognized that mapping is a complex problem, so IDNA 2008 didn't tackle the mapping problem, suggesting that different folks could implement their own appropriate mappings.

Clearly it doesn't help much to have everyone doing their own different mapping, so Unicode provided a mapping which was influenced heavily by the mappings of IDNA 2003 for compatibility.  I'm not quite sure how U+0130 ended up with its peculiar mapping, which seems like a quirk or the order the rules are applied.  Though I find that particular mapping confusing, it is consistent with IDNA2003.

> I think we have to worry about cases where input strings are the result of mapping, yes, but _before_ we tackle the really hard cases can we sort out the merely hard cases?

Hmm