How to compress XML/RSS data?

[Sportman]

To compress an XML file for example an RSS feed, what kind of
compression can be useful when?

1. Only compress date between elements.
2. Compress also the elements but keep elements searchable.
3. Compress the total feed (elements not searchable).

Or are there smarter ways to store date logical as in a RSS feed with a
total different concept for example a static reference library what's
needed to read feed data.

Interesting is size, speed and in combination with possible HTTP GZIP
compression what some web servers already support.

I was triggered because Microsoft has big plans with RSS
http://news.zdnet.com/2100-9588_22-5759366.html but is uncompressed RSS
the best possible way to store the future world data?

[Sportman]

Typos: date must be data