Rationale problems

[Paul Hoffman]

At 11:31 AM -0500 12/6/08, John C Klensin wrote:
>--On Saturday, 06 December, 2008 16:14 +0100 Harald Tveit
>Alvestrand <harald at alvestrand.no> wrote:
>
>> The other difference is that when a character is UNASSIGNED in
>> the user's current Unicode installation, he can use it for
>> exactly nothing, so it will not be surprising to him that he
>> can't use it in domain names either.
>> For instance, he won't be able to see it in an e-mail
>> containing an URL that uses the newly assigned character until
>> he upgrades his font libraries to support the new character.
>>
>> On the other hand, if a character is DISALLOWED on his system,
>> he might still see it, be able to type it and use it in other
>> contexts. Seeing inconsistent behaviour for whether or not he
>> is able to use it in a domain name will be more surprising.
>> User astonishment is usually a Bad Thing.
>
>Yes, indeed.

I will disagree here. Unassigned characters can easily be used in many applications: they just show up with the "unknown glyph" glyph. Users do not know when a character that they copy-and-paste, for example, is unassigned or just doesn't have a glyph on their current system.

I agree with John's earlier assessment:

At 9:57 AM -0500 12/6/08, John C Klensin wrote:
>One could make much the same argument about not looking up
>UNASSIGNED characters.  When a new character is added to Unicode
>whose properties would cause it to be PVALID, one has to wait
>until
>all lookup software is updated before that character is reliably
>available.

Users will have no idea if characters are DISALLOWED or UNASSIGNED.