How does apache handle caching of certain files, and is it possible to explicitly say that certain files should be aggressively cached more than others, through the standard config files for a given host or virtualhost?

To put it in context, I keep a lot of site content in various XML files, and I'd like to be able to say that this file will be used a lot, and therefore cache it as much as possible..? Does apache do this kind of thing intelligently and on the fly..? Will it observe which files are more popular than others and try to match cache hits appropriately..?

Lots of questions in one, but the basic idea should be clear enough.

edit: to be clear, these are resource files which are loaded and interpreted by PHP - but php as a process is spawned inside apache.. right? Please help!