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HTML authors can put tags in a document's <HEAD> section that describes its attributes. These Meta tags are often used in the belief that they can mark a document as uncacheable, or expire it at a certain time.
Meta tags are easy to use, but they aren't very effective. That's because they 're usually honored by browser caches (which actually read the HTML), not proxy caches (which almost never read the HTML markup in the document). While it may be tempting to slap a Pragma: no-cache meta tag on a home page, it won't necessarily cause it to be kept fresh, if it goes through a shared cache.
On the other hand, true HTTP headers give you a lot of control over how both browser caches and proxies handle your objects. They can't be seen in the HTML, and are usually automatically generated by the Web server. However, they can be controlled to some degree, depending on the server it's used.
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Copyright © 2003, John Yannakopoulos <giannak@csd.uoc.gr>