XMLdsig Comment about multiple SignerInfo to support multiple signers

Hello!

    I have been reading the XML signature specification and I many 
things is similiar to the CMS standard. However, there are some aspects 
that are different. I wonder why in a XML Signature can not be signed by 
several signers, inserting several SignedInfos (cosign in CMS). I think 
this case is very interesting in the contract signing. Something 
similiar could be done with XAdES and the counter signature. However, I 
thing I would be better to be able to have several signerInfos in the 
signature element.

What do you thing about this?

Regards.