M-label definition

[Cary Karp]

> Under IDNA2008, with the way the documents are today, it is an
> M-label because the "ß" character is PVALID.
> 
> What causes you to think otherwise?

I was commenting on the inapplicability of the new term to the full 
battery of codepoints that are remapped under IDNA2003 (which removes ß 
from the IDN space entirely). Since we haven't discussed any other 
mapping rules, and ß appears to be the focus of particular concern on 
this list, I suppose I was looking for some reassurance that we are 
beyond questioning its PVALID status in IDNA2008.

I also feel it might be useful if the descriptive framework we're 
developing for IDNA2008 is, itself, backwards compatible.

/Cary