Compound operation Verify & Sign

Following the discussion on the <Status> element brings to mind the
discussion we had a few meetings ago on compound (or what Ed called stacked)
operations and particularly the ability to support a VerifyAndSign operation
where a counter signature is applied based on whether the original signature
is valid.

I believe that such an operation is important in a number of use cases, for
example, notarisation services.

This was brought up at the F2F meeting and was included in the requirements
document (3.9).  My recollection of the discussion on 22 Sept is that the
only compound operation that was needed would be VerifyAndSign, although I
see no record of it in the minutes.

How do we envisage VerifyAndSign being supported in the DSS protocol?  Is
there a way of combining the two request / response structures, or do we
need to define a specific structure which is this combined operation?

Nick