> > But there is one class of characters that might indeed be
> dreadful at
> > the beginning: combining characters. I recently refered to labels
> > that begin with combining characters as invalid Unicode strings, but
> > they're not, are they? They just behave in surprising ways when
> > abutted with something else. Maybe nameprep should prohibit initial
> > combining characters.
>
> Note that these are rules for hostnames in particular.
>
> A prohibition against combining characters is not feasible. See
> <[EMAIL PROTECTED]> from K Whistler.
>
> This was resolved without disconsent in <[EMAIL PROTECTED]>:
>
> | First and last characters in the label MUST NOT be a diacritical
> | mark or hyphen-minus.
I agree that having a combining character as the first character
in a hostname part (label) is a bad idea (nominally it combines with what
is before it and can in rare cases be "absorbed" into syntax before
the acutal string (like in >/, for xhtml, where / is combining long solidus;
after NFC (applied blindly to the entire text) there will be a precomposed
negated greater than character there...)
But I see absolutely no reason to prohibit combining characters
at the end of a label (unless applied to a hyphen-like character...).
Kind regards
/kent k
