Prohibiting mapping of PVALID characters

Paul Hoffman phoffman at
Wed Dec 9 23:04:41 CET 2009

At 5:00 PM -0500 12/9/09, John C Klensin wrote:
> > Depending on local needs, this conversion may involve coding
>> conversions. The conversion may also involve mapping some
>> characters; however, such mapping MUST NOT be applied to any
>> character that has a type of PVALID, regardless of the local
>> needs.
>> The problem with this is that it makes a MUST-level
>> requirement that is begging to be broken ("our needs for
>> mapping are greater than our needs for conformance to the
>> RFC"). But it might be the best we can do.
>Yes, that is probably the right place and just about the right
>text (assuming the WG wants to do anything at all).   The reason
>why I suggested SHOULD was to avoid making a MUST-level
>requirement that, as you put it, is begging to be broken.  But
>MUST may still be the best answer, if only because SHOULD would
>probably require an explanation that the WG might have some
>difficulty agreeing on.

In writing my proposed rewording, I could not think of any explanation of the SHOULD that would be clear to the reader. I do not think "if you find it important" to be clear. Maybe others can be more creative than I was.

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