Punycode Mixed-case annotation

Vint Cerf vint at google.com
Sun Jun 28 13:26:05 CEST 2009


If we adopt a policy of mapping prior to look up, and if we map upper  
case to lower case,
it may be that xn--RSUM-bpad.com will be changed to xn-rsum-bpad.com  
prior to lookup and it will work.


On Jun 28, 2009, at 7:20 AM, Wil Tan wrote:

> Hi folks,
> RFC3492 contained a mixed-case annotation feature which, though not
> used in IDNA2003, may affect the IDNA2008 specs. In particular, basic
> code points ([a-z]) that are left unencoded in punycode may be
> substituted in upper case, and the result of ToUnicode operation will
> preserve them. For example,
>  ToUnicode("xn--RSUM-bpad.com") = "RéSUMé.com"
> From reading the rationale and protocol drafts, I'm not entirely sure
> if the input is considered an A-label. The output is certainly not a
> U-label since "RSUM" are disallowed codepoints.
> I don't know if this is a problem, but it may warrant at least some
> discussion in section 5.4 of idnabis-protocol?
> =wil
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