Compiled XML

Hello All,

I'm new to the xml-dev list, so please forgive (and point out) any stupid
mistakes :P
The possibility occurred to me the other day that some applications,
particularaly those that can send a large number of messages frequently (eg,
peer-to-peer programmes) and those with low-bandwidth connections, would
benifit from a 'compiled' or 'compressed' form of XML - one in which as much
empty space and repetition as possible has been eliminated. The form of
compiled XML I was envisaging would have two main aims: 1) To decrease
message size, and 2) To make messages easier to parse & read.
I have come up with further ideas on this scheme, but I'd first like to know
a couple of things: Has this been done before (And if so, can someone point
me to it?), and is something like this a standard in the making?

Thanks,

Nick Johnson