SyncML is kind of interesting

[Tim Bray <tbray@textuality.com>]

 Check out http://www.syncml.org/

There are a lot of heavyweights behind this.  Looks like a
nice sensibly-designed language, not that I know anything
about syncing PDAs.

Interestingly, their namespace URI points at a DTD 
(although SyncML messages need not be valid), and yet
the page at http://www.syncml.org/downloads.html seems like 
strong evidence why something like RDDL is a good idea.

Sadly, they allow WAP's binary-XML representation, although 
it seems obvious that there are better ways to compress XML 
than replacing tags with numbers.  -Tim