Q2: What mapping function should be used in a revised IDNA2008 specification?

[Paul Hoffman]

At 4:30 PM -0400 4/1/09, John C Klensin wrote:
>Of course, if we use mapping strictly to ensure IDNA2003
>compatibility for reasonable cases, rather than making up new
>ways to turn code points into other code points, that is a
>non-issue because the table will be fixed once and never change.

The WG did not agree that mapping was only to ensure IDNA2003 compatibility.

> > At 1:41 AM -0400 4/1/09, John C Klensin wrote:
>>> Under no circumstances should mapping be used as a mechanism
>>> for undoing those decisions, i.e., mapping should be
>>> permitted only when the result is a PVALID character.
>>
>> If you meant "PVALID, CONTEXTJ, or CONTEXT0", I agree.
>
>While I could live with the broader definition, I note that none
>of the characters that are now handled as CONTEXTJ or CONTEXTO
>are now valid under IDNA2003.  I might have missed something,
>but a scan of the UnicodeData table seems to indicate that none
>of them are the targets of compatibility mapping either.  So,
>because I still see the use of mapping as transitional, I
>deliberately chose the narrower and less complex statement.

OK, then we disagree here. I do not think it is wise for us *now* to say that the characters in CONTEXTJ and CONTEXTO will not change before the spec is finished.