Errm, XML import?

I've seen all over newsites have these XML files you can either download, or connect to, and they let you update your site with their headlines...One example, on /. (slashdot)...
http://slashdot.org/code.shtml

read Importing of Slashdot headlines

I'll be using PHP to do it, but was wondering how these XML files work as well..

THanks in advance, and if this is too broad, do tell https://www.sharkyforums.com/images/.../2005/06/6.gif


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