I know, I am horribly moving out of the scope of thread. Sorry about that. If I recall correctly, which admittly I rarely do, a webserver should "rebuild" server includes and actually the whole HTML page, if the header of the page demands it in the expire attribute of the META tag. The HTTP1.1 specs has this to say about it. For examples of the META tag and expire dates, you can see W3C's description of it. That should take priority over file size, modifications dates and the like.