With regards to how to handle multiple body parts in any SIP message, I believe 
the issue we're concerned with is how to handle body-parts that are not for the 
actual context of the SIP message, in a backwards-compatible way, right?

In other words, the context for bodies by default is based on their message 
method type, and possibly package if the method type has packages (SUB/NOT/PUB, 
and now INFO).  And since for 3261 the Content-Disposition's default means 
"render" (unless C-T is app/sdp), then no C-D means render - where "render" has 
different meanings based on the context too.  For MESSAGE/INVITE/BYE it's 
basically render to the user in some fashion; for package ones it's render to 
the package application, which effectively is the "user" of the message.  Right?

So ISTM that the body-handling draft does that.  For new extensions going 
forward it would be done with a Content-ID and a C-D of "by-reference" in MIME, 
with a SIP header using a CID.  For older extensions it's handled by the option 
tags they already define, to make sure the recipient understands the extension 
and thus its additional body part's context. (I don't like that, but that's 
life)  And it's only really a problem for cases where the content-type collides 
with something valid for the message's context/package.

So I'm back to: this is no different for INFO.  INFO has a context, we're 
adding a sub-context with Info-Package to fix collisions of same content-types 
for different uses, and any SIP extension going forward uses a CID and 
content-id and C-D of 'by-reference' if it's not tied to the message's context. 
 The Info draft only needs to reference the body-handling draft, call out the 
fact that INFO and its Info-Package creates a context, and a quick reminder on 
what that means.  We can then pull out all the current text about bodies in the 
draft, including the cid parameter and such, and move on to more interesting 
things like responses and actually defining packages. :)

-hadriel
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