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<DIV>As suggested to me, here are the changes to the IDNA documents that I hope
will clarify things with combining characters:</DIV>
<DIV> </DIV>
<DIV>"4.2.3.2 Leading Combining Characters</DIV>
<DIV> </DIV>
<DIV>The Unicode string MUST NOT begin with a combining character (as defined in
The Unicode Standard, Section 3.6 [Unicode])."</DIV>
<DIV> </DIV>
<DIV>"Labels whose first character is a combining character (as defined in The
Unicode Standard, Section 3.6 [Unicode])."</DIV>
<DIV> </DIV>
<DIV>Note that:</DIV>
<DIV> </DIV>
<DIV>- The RFC uses both "combining mark" and "combining character"; it is
better to use just one of these terms, since they mean virtually the same
thing.</DIV>
<DIV>- There are two plausible definitions of a "combining mark" or "combining
character": a character with a non-zero canonical combining class, or a
character with general category of Mn, Mc, or Me. Since the term
"combining character" has the latter definition in the Unicode Standard and the
term "combining mark" is also used, I believe this is what is meant.</DIV>
<DIV>- Some of the characters affected by the two definitions include Indic
consonant and vowel signs, variation selectors, subjoined letters, and the
Combining Grapheme Joiner. All of these have combining class 0 and a
general category of Mn, Mc, or Me, and the vast majority of them are in the
PVALID category. I'm not aware of any registries that allow labels
that begin with those characters.</DIV>
<DIV> </DIV>
<DIV>--Peter</DIV></DIV></DIV></BODY></HTML>