[idn] Prohibiting characters in draft-ietf-idn-nameprep

[Paul Hoffman / IMC <phoffman@imc.org>]

Greetings. After the discussion in Pittsburgh on the nameprep draft, 
Marc and I have an open issue on when to prohibit characters.

The current document has the order of processing looking like:
1) Check for prohibited input (many)
2) Fold case
3) Canonicalize with normalization form KC

A possible alternative has been proposed that adds a step:
1) Check for prohibited input (a few, just for case)
2) Fold case
3) Canonicalize with normalization form KC
4) Check for prohibited output

I believe that the proposed alternative is a good one, even though it 
complicates the processing some by having two lists. The advantage is 
that it would disallow fewer characters on input, and therefore cause 
less surprise for users.


--Paul Hoffman, Director
--Internet Mail Consortium