Content-free Header and Body elements

Are the following messages semantically equivalent (namespace 
declarations omitted for brevity)?
   <S:Envelope>
      <S:Header></S:Header>
      <S:Body><tns:foo/></S:Body>
   </S:Envelope>
and
   <S:Envelope>
      <S:Body><tns:foo/></S:Body>
   </S:Envelope>

In other words, if there are no headers, are message processors allowed 
to insert/delete an empty Header element?  I believe the answer is yes, 
as I can't find text that says otherwise.

And what if there are no EII's for the Body, can that be omitted?
   <S:Envelope>
      <S:Header><tns:foo/></S:Header>
   </S:Envelope>
and
   <S:Envelope>
   </S:Envelope>

This has implications for message normalization and the ability to sign 
SOAP messages.
	/r$
-- 
Rich Salz, Chief Security Architect
DataPower Technology         http://www.datapower.com
XS40 XML Security Gateway    http://www.datapower.com/products/xs40.html