[JDEV] How to evolve a namespace or protocol?

[chelck at ebs.com]

A general question. Suppose I define a new message protocol and a new name 
space. I modify my Jabber server and clients to handle this protocol. I 
distribute the new client to all my customers. Later on I decide to change my 
protocol, how do I do this without breaking the existing clients in the 
field?

I assume I use version numbers of some sort, but I'm not sure where or how. 
Will my message have to contain multiple versions of the same data?

A real world example would be helpful.

Thank you,
Christopher Helck
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