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<DIV><FONT size=2 face=宋体></FONT> </DIV>
<DIV><FONT size=2 face=宋体>+1.</FONT></DIV>
<DIV><FONT size=2 face=宋体></FONT> </DIV>
<DIV><FONT size=2 face=宋体>good point: "</DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif">So it is best to just
avoid a mention of a limit like 252; either that or explain the situation in
more detail.</FONT></DIV>
<DIV>"</DIV>
<DIV> </DIV>
<DIV>good example: <FONT face=Georgia>Repeat it(U+01DE ( Ǟ ) ) 57
times. That is of length 684.</FONT></DIV>
<DIV><FONT face=Georgia></FONT> </DIV>
<DIV><FONT face=Georgia></FONT> </DIV>
<DIV><FONT face=Georgia>Jiankang Yao</FONT></DIV>
<DIV></FONT> </DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV style="FONT: 9pt 宋体">----- Original Message ----- </DIV>
<DIV style="FONT: 9pt 宋体; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=mark@macchiato.com href="mailto:mark@macchiato.com">Mark Davis ☕</A>
</DIV>
<DIV style="FONT: 9pt 宋体"><B>To:</B> <A title=klensin@jck.com
href="mailto:klensin@jck.com">John C Klensin</A> </DIV>
<DIV style="FONT: 9pt 宋体"><B>Cc:</B> <A title=mscherer@google.com
href="mailto:mscherer@google.com">Markus Scherer</A> ; <A
title=idna-update@alvestrand.no
href="mailto:idna-update@alvestrand.no">idna-update@alvestrand.no</A> ; <A
title=kenw@sybase.com href="mailto:kenw@sybase.com">Kenneth Whistler</A>
</DIV>
<DIV style="FONT: 9pt 宋体"><B>Sent:</B> Thursday, September 30, 2010 9:31
AM</DIV>
<DIV style="FONT: 9pt 宋体"><B>Subject:</B> Re: Potential Erratum re. length
limits in RFC 5890</DIV>
<DIV><BR></DIV><FONT class=Apple-style-span face="georgia, serif">Ken is right
about the maximal source label length being at least 252 in the absence of
mapping. </FONT>
<DIV><FONT class=Apple-style-span face="georgia, serif"><BR></FONT></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif">With the use of
mapping, however, it could be substantially longer. This can happen a
series of characters in the source can map to a single character, and then are
mapped to a single byte in Punycode. That can happen with IDNA2008, or with
UTS46 (or any other mapping preprocessing for IDNA2008).</FONT>
<DIV><FONT class=Apple-style-span face="georgia, serif"><BR></FONT></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif">So it is best to just
avoid a mention of a limit like 252; either that or explain the situation in
more detail.</FONT></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif"><BR></FONT></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif">====</FONT></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif"><BR></FONT></DIV>
<DIV><FONT class=Apple-style-span
face="georgia, serif">Details. </FONT><SPAN
style="FONT-FAMILY: georgia, serif" class=Apple-style-span>As illustration,
suppose that you had the following, in UTF32.</SPAN></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif"><BR></FONT>
<DIV><FONT class=Apple-style-span face="georgia, serif">00 00 00 41 00
00 03 08 00 00 03 04</FONT></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif"><BR></FONT></DIV>
<DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif">That sequence, when
normalized to NFC, yields </FONT></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif"><BR></FONT></DIV>
<DIV><FONT class=Apple-style-span
face="georgia, serif">U+01DE ( Ǟ ) LATIN CAPITAL LETTER A WITH
DIAERESIS AND MACRON, one character. </FONT></DIV></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif"><BR></FONT></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif">Repeat it 57 times.
That is of length 684.</FONT></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif"><BR></FONT></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif">When normalized under
NFC, you get </FONT></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif"><BR></FONT></DIV>
<DIV><FONT class=Apple-style-span
face="georgia, serif">ǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞǞ<BR></FONT>
<DIV><FONT class=Apple-style-span face="georgia, serif"><BR></FONT></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif">That turns into the
valid Punycode:</FONT></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif"><BR></FONT></DIV>
<DIV><SPAN style="FONT-SIZE: 13px" class=Apple-style-span><FONT
class=Apple-style-span
face="georgia, serif">xn--bkaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa</FONT></SPAN></DIV>
<DIV><FONT class=Apple-style-span face="georgia, serif"><BR></FONT></DIV>
<DIV>
<DIV>
<DIV>
<DIV><FONT class=Apple-style-span
face="georgia, serif">Mark<BR><BR></FONT></DIV></DIV></DIV></DIV></DIV></DIV></DIV></BLOCKQUOTE></BODY></HTML>