New WS-SecurityPolicy Issues

a) Should the sp:SignedParts mechanism (lines 592-605) allow specification 
of header elements targeted to a specific s11:actor or s12:role?

b) Should the sp:RequiredElements mechanism (lines 735-740) allow 
specification of otherwise optional elements that are not children of 
soap:Header?

c) Should there a be way to specify that a signature reference for a given 
SignedPart or SignedElement must use an absolute XPath expression?