referencing IDNA2008 (and IDNA2003?)

John C Klensin klensin at
Fri Oct 22 21:23:14 CEST 2010

--On Friday, October 22, 2010 22:03 +0330 Alireza Saleh
<saleh at> wrote:

> So what happened if someone types a vali PunyCode but with
> capital letters as an address.

Do you mean "Something that looks like an A-label with one or
all letters in capitals"?  If so, it isn't a valid IDNA2008
A-label. However, for IDNA2003 compatibility, I would strongly
recommend lower-casing ASCII strings that appear to be A-labels
before processing them) -- fortunately, one of the few things in
this space we are pretty sure we know how to do is to convert
all-ASCII strings to lower case.  :-)

If you mean "something that looks like a U-label but that
contains letters in capitals", it is invalid under IDNA2008 (See
Rule B, Section 2.2 of RFC 5892).  It would be valid under
IDNA2003 (because case folding is built into Nameprep), but
cannot be derived by applying ToUnicode to a valid string
produced by ToASCII (more or less an A-label).

So I'm not quite sure what you mean by "valid PunyCode".


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