Re: [precis] Enforcement as an Idempotent operation

Peter Saint-Andre <stpeter@stpeter.im> Mon, 27 February 2017 00:48 UTC

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To: William Fisher <william.w.fisher@gmail.com>
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From: Peter Saint-Andre <stpeter@stpeter.im>
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Date: Sun, 26 Feb 2017 17:48:45 -0700
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Subject: Re: [precis] Enforcement as an Idempotent operation
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On 2/13/17 12:04 AM, William Fisher wrote:
> On Sun, Feb 12, 2017 at 12:27 PM, Peter Saint-Andre <stpeter@stpeter.im> wrote:
>> Did you mean U+212A (KELVIN SIGN)? That decomposes to U+004B (LATIN CAPITAL
>> LETTER K).
>>
>>> The full example is:
>>> "\U0001f11aevin" => "(K)evin" => "(k)evin"
> 
> I'm talking about 'PARENTHESIZED LATIN CAPITAL LETTER K' (U+1F11A).
> Sorry it's not clear that the A is part of the unicode escape.

Thanks for the clarification.

> With casefold or tolower, the result is the same for these Nicknames:
> 
> Not idempotent: "\U0001f11A" => "(K)" => "(k)"
> Not idempotent: "\U0001f13A" => "K" => "k"
> Not idempotent: "\u210c" => "H" => "h"
> Not idempotent: "\u210d" => "H" => "h"
> Not idempotent: "\u20a8" => "Rs" => "rs"
> 
> When you apply the comparison steps from RFC 7700, Section 2.4, you
> still get something that is upper case. If you apply the comparison
> steps again, you now get lower case.

I see what you mean. I'm now leaning toward moving the case mapping rule
after the normalization rule, but first I want to think about the
implications for all of the PRECIS profiles (e.g., when using NFC vs.
using NFKC). If we go down this road, we will also want to describe the
reasoning in Section 5.2.3 of 7564bis.

Peter