"As Web pages become more database-driven and dynamic, it is important that Web browsers display the most up-to-date information available from your site. For those who have been in the PHP field for some time, dealing with this issue is nothing new. The problem itself has nothing to do with PHP at all. Rather, it is the client's browser that is the source."

"... In order to ensure that the Web browser will always download new content, rather than simply relying on its cache, the proper HTTP Headers must be sent before any content. These headers -- "Expires", "Last-Modified", "Cache-Control", and "ETag" -- are used to implement a cache negotiation with the browser in such a way that allows the content to be updated if the document has truly been modified. It still allows the use of the cache if it has not (saving on transfer times). We'll look at these header commands and how they work, to guarantee that content that is updated is refreshed as expected."

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