Prohibiting mapping of PVALID characters

[Cary Karp]

> So unless the protocol document defines "mapping" somehow
> more restrictively to mean "the kinds of mappings we don't
> want in the protocol, i.e., case mappings, *compatibility*
> normalization mappings, etc., as opposed to the kinds
> of mappings we *require* in the protocol, i.e. *canonical*
> normalization mappings", I see this as just introducing
> more potential for confusion in the protocol statement.

What happens if we take a first cut at recognizing this by adding 
something along the lines of "... no mapping of PVALID characters 
(except for the changes implicit in NFC normalization) ..." wherever 
appropriate?

/Cary