Re: [idn] I-D ACTION:draft-ietf-idn-vidn-00.txt

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

It looks like VIDN can be thought of as a non-reversible ACE, that is, a
VIDN is a many-to-one map from international strings to valid host name
labels, whereas the other ACE schemes have all been one-to-one maps.

The advantage of using a many-to-one map is that it can be simpler,
and because it's less constrained, the host name label can be somewhat
intelligible.

One advantage of using a one-to-one map is that it avoids collisions.
With VIDN, you might be unable to register a string even if no one is
using that string, just because someone is using some other string in a
different language that happens to map to the same host name label.

To see another advantage of using a one-to-one map, consider the From:
address of an email message.  In order for the recipient to be able to
reply, the address must use a valid host name (containing only ASCII
letters, digits, hyphens, and dots).  If the map is reversible, the
recipient's mail program can convert it back into the original language
for display purposes, but this is not possible if a many-to-one map is
used.

AMC