[Dime] The M-bit MAY column issue

["Tschofenig, Hannes (NSN - FI/Espoo)" <hannes.tschofenig at nsn.com>]

Hi all, 

the M-bit setting in an AVP indicates what the receiving side has to
understand. From an implementation point of view there are only these
two options:  
* I have to implement the AVP.
* I don't have to implement it. It's optional.  

For the sending side the ABNF tells what the sender has to put into a
command (with some additional constraints). 

When one restricts the M-bit setting to 
-- MUST and 
-- MUST NOT 
then the semantic regarding what has to be implemented and understood is
essentially determined at the time when the specification was written
and this raises the question about why that information is carried in
the protocol itself (rather than just written in the specification very
much like the ABNF is).

Some folks in the past suggested to remove the MAY option of the M-bit.
My question is: Why is the M-bit flag in the AVP needed at all?  Why
don't we replace it with a table in the document that says which AVPs
must get implemented and which others are optional? 

Ciao
Hannes
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