[Standards] dialback: piggybacking

[Philipp Hancke]

Justin Karneges wrote:
> Of all the places in Jabber to value backwards compatibility, dialback is 
> arguably the most important.  IMO, the real trouble is not the implementation 
> difficulty, but the fact that dialback is underspecified in the RFCs.  Let's 
> get this thing fully specified in the bis drafts, and then I agree with 
> Matthias: MUST for receiving and MAY for sending is the most compatible path 
> to take.

Is it necessary to specify the gory details of when-to-send in the bis
drafts or would it be sufficient in a XEP?

Philipp