idna-mapping update

[Paul Hoffman]

If we re-open -mappings, it should only be to weaken any implied recommendation of its universality, not to fine-tune the barely-proposed transform. Michel is correct that the fact that it exists will cause some people to think that it is recommended by the IETF, regardless of its IETF status. However, history has shown that there is *nothing* we can do to change that perception for many readers.

One change that the WG might consider making to -mappings is to replace section 2 with "do it like in TR46". I don't think this is necessary because that's what TR46 already says. Another change would be to say "map just like in IDNA 2003, but with more recent tables"; that option didn't go over so well earlier in this WG. :-)

The main purpose of -mappings is to emphasize the lack of requirements for mapping, not which one might be good. If there is some more wordsmithing to section 1 to make that even clearer, we could do that, but changing the document to say "this document has no real requirements, but you might want to consider doing mappings that are that document over there that has many requirements" would cause more confusion about what the IETF meant, not less.