Re: [idn] Should we add U+FF0E FULLWIDTH FULL STOP to section 5. 10 of Nameprep?

["Adam M. Costello" <amc@cs.berkeley.edu>]

Yves Arrouye <yves@realnames.com> wrote:

> I wasn't really clear.  Since it's forbidden because of the
> compatibility mapping, all I want is some text that identifies that as
> a caveat for IDN implementers, so that they don't just map U+3002 to
> U+002E before Nameprep and then wonder why this one doesn't work.

I'm still not sure what you want, but I just noticed that the existing
explanation of the prohibition of U+3002 is a bit misleading.  It
currently says:

    U+3002 is used as if it were U+002E in many input mechanisms,
    particularly in Asia.  This prohibition allows input mechanisms to
    safely map U+3002 to U+002E before doing nameprep without worrying
    about preventing users from accessing legitimate host name parts.

However, mapping U+3002 to U+002E "before doing nameprep" isn't specific
enough.  If it happens immediately before doing nameprep, then nameprep
will fail.  It needs to happen before the domain name is split into
labels.  Therefore I think the text should read:

    U+3002 is used as if it were U+002E in many input mechanisms,
    particularly in Asia.  This prohibition allows input mechanisms to
    safely map U+3002 to U+002E before splitting a domain name into
    labels, without worrying about preventing users from accessing
    legitimate host name parts.

This recalls an earlier discussion about just how much processing
should be done before a domain name is split into labels.  Should
fullwidth-full-stop be mapped to full-stop before the splitting?
Probably.  How about one-dot-leader (for which full-stop is a
compatibility decomposition)?  Maybe.  Should digit-one-full-stop be
replaced by its compatibility decomposition "1."?  Or square-CO by its
compatibility decomposition "CO."?  Maybe not.

Should this be left up to the user interface designer, or should there
be recommendations or requirements?

AMC