Agreed. I just came to the same conclusion too.<br><br><div class="gmail_quote">2009/8/31 John C Klensin <span dir="ltr"><<a href="mailto:klensin@jck.com">klensin@jck.com</a>></span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<br>
<br>
--On Monday, August 31, 2009 07:10 +0200 Patrik Fältström<br>
<div><div></div><div class="h5"><<a href="mailto:patrik@frobbit.se">patrik@frobbit.se</a>> wrote:<br>
<br>
><br>
> On 31 aug 2009, at 07.05, Patrik Fältström wrote:<br>
><br>
>> So, casefold of the ascii in the A-label only result in<br>
>> casefold of the ascii in the U-label.<br>
><br>
> Ok, after a gulp of coffee, I see your point.<br>
><br>
> In the tables document we have the following:<br>
><br>
>> 2.5. LDH (E) E:<br>
>><br>
>> cp is in {002D, 0030..0039, 0061..007A}<br>
><br>
> That make for example 'F' illegal in an U-label.<br>
><br>
> By changing this rule to the following, uppercase ASCII would<br>
> be ok to have in an U-label.<br>
><br>
> 2.5. LDH (E) E:<br>
><br>
> cp is in {002D, 0030..0039, 0041..005A, 0061..007A}<br>
<br>
</div></div>But that would be a mistake, IMO, because it would result in<br>
U-labels containing uppercase ASCII that produce different<br>
A-labels from the same U-label with lowercase ASCII. Those<br>
A-labels would match in the DNS, which uses case-insensitive<br>
comparison, but not in ordinary string comparisons (because they<br>
are different).<br>
<br>
Put differently, that would give us a pair of U-labels that do<br>
not compare equal on bitstring comparison (the only kind of<br>
comparison defined for U-labels) but which produce equivalent<br>
(although not identical) A-labels. And, because of the<br>
compression "feature", we would lose unambiguous symmetry of<br>
A-labels and U-labels because, depending on where it came from,<br>
a given A-label (and its DNS-equivalents) could produce<br>
different U-labels.<br>
<br>
This would also imply that<br>
"Fältström" and "fältström"<br>
would be valid U-labels but that "FÄLTSTRÖM" would not be<br>
because Ä and Ö are both DISALLOWED. I don't think we want to<br>
go there.<br>
<font color="#888888"><br>
john<br>
</font><div><div></div><div class="h5"><br>
<br>
<br>
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</div></div></blockquote></div><br><br clear="all"><br>-- <br>Wil Tan<br>CTO<br>Cloud Registry <<a href="http://www.cloudregistry.net">http://www.cloudregistry.net</a>><br>