Steve,
Procedural note, concerning extensions and alternatives:
It seems to be common practise to write a spec which has a) the framework for
doing
a set of things, b) details concerning one or more alteratnives, and c)
reference to
IANA registration for any extensions beyond the current doc.
Including one or more explicit alternatives makes the framework more concrete.
Having more than a few clutters things up.
IANA does not require RFC publication, tho it is of course encouraged. But it
does require explicit documentation. Postel can clarify.
My guess is that you will want the IANA registration to be for a full-set of
details, per alternatives.
That is, DS, H, C, D all together, to make sure that people don't try silly
combinations.
Dave