Re: [Editorial Errata Reported] RFC4013 (1812)

[Alexey Melnikov <[e-mail]>]

Jeffrey Hutzelman wrote:

> --On Wednesday, July 22, 2009 08:20:34 PM +0200 Simon Josefsson 
> <[e-mail]> wrote:
>
>> RFC Errata System <[e-mail]> writes:
>>
>>> Section: 2.3
>>>
>>> Original Text
>>> -------------
>>> Section title is "Prohibited Output"
>>>
>>> Corrected Text
>>> --------------
>>> Section title should be "Prohibited Input"
>>>
>>> Notes
>>> -----
>>> Section 2.3 is talking about prohibited input, not prohibited output.
>>
>> I'm not sure about this -- compare RFC 3454 section 5, the terminology
>> and design is about prohibiting code points in the _output_.
>>
>> Testing for code points in the _output_ may be semantically different
>> from testing in the _input_.  Some other IDNA operation may modify code
>> points into one of the prohibited _output_ code points.  See RFC 3454
>> section 2, the map&normalize steps are taken before the prohibit step.
>
> I agree with Simon here.  Prohibiting a code point in the output 
> usually has the effect of making any input containing that code point 
> result in a failure, but the point is that the _output_ will never 
> contain that code point, even as the result of mapping and 
> normalization -- the operation will fail instead.  This distinction 
> was a conscious decision made in stringprep.

Agreed.

> There is, however, an error -- the first sentence of this section does 
> in fact claim to be specifying prohibited input characters.  The 
> correct fix is to that text, not to the section title.

My understanding is that prohibited characters are never generated 
during mapping.