[idn] Newbie's questions implementing the [IDNA]

[Seungho Lee <shlee@netpia.com>]

Hello.

Implementing [IDNA] spec, I found an incomprehensible parts,
so I ask for your helps...

Question1.
What kind of sequence of code points can be the input of ToUnicode 
Operation?
Only punycoded one or all the other ones?
If in case of only punycoded one, it seems that the [NAMEPREP] operation 
is unnecessary...
(They will be in the ASCII range...)
And if all the other ones are permitted, isn't it that the [NAMEPREP] 
can't convert it to punycoded one?
(There is no punycode encoding process in Step2,
and From Step3, it is solid that the input is the ACE code points 
starting with ACE prefix.)

Question2.
What is the return value of DNS?
I think it is the IP address just like the usual DNS return value...
For example, when I send the query 'PREFIX-089a.com'(this is a Korean 
character) to the resolver,
the DNS will return the IP address for 'PREFIX-089a.com', won't it?

But the [IDNA] spec says in page 3,
- The ToUnicode opeartion is used when displaying names to users,
for example "names obtained from a DNS zone".

Does the DNS return a name?

Question3.
I came to think that the ToUnicode opeation is not included in the major 
flow of 'sending query and receiving the return values'.
This is the flow I pictured... (only when a person is to use IDN for web 
surfing...)
1) An user inputs an IDN to the browser... ( Let's suppose the input was 
'?.com' )
2) The IDNA client program takes the input.
3) Through the conversion operation ( the Step 4 would be ToASCII ), the 
input is changed to a punycoded one.
( '?.com' is converted to 'zq-089a.com' ; suppose the prefix is 'zq--' )
4) The IDNA client program sends the query to the resolver.
5) The resolver sends the query to the designated name server.
6) The name server sends the query to the .com name server.
( Suppose the user-designated name server has no cache for the query and 
also is not the authoratitive name server)
7) .com name server sends the query to the zq--089a.com name server.
8) The zq--089a.com name server returns the IP address.
9) The client's resolver receive the return value(IP address)

So, even though ToUnicode indispensible process of [IDNA], (because the 
spec requires that the uses should not see
the incomprehensible punycoded names), I think it is outside the major 
flow of 'sending query and receiving the reutrn values'...

Is this an acceptable thought?

And where exactly the ToUnicode operation should be done?
Between 3) and 4)?


Regards,
Lee
-----
Seungho Lee
Netpia.com, Korea.