Setting both Expires and Cache-Control: max-age

Question

Can someone clarify this statement about caching.

https://developers.google.com/speed/docs/best-practices/caching says

It is redundant to specify both Expires and Cache-Control: max-age, or to specify both Last-Modified and ETag.

Then later it says

The fingerprinting mechanism allows the server to set the Expires header to exactly one year ahead of the request date; the Last-Modified header to the date the file was last modified; and the Cache-Control: max-age header to 3153600.

This latter statement goes against the prior -- about not setting both the Expires and Cache-Control.

Is the first statement the norm, and the second an exception? Or is this doc simply going against it's own recommendations? What's suggested?

Thanks.

Answer 1

[Cache-Control:max-age] and [Expires] in Http are doing the same thing and that is a reason why they are redundant. But there are still some big differences between them, [Cache-Control] is http/1.1 standard and Expires is http/1.0. If client browser does not support http/1.1 Cache-Control will be ignored, and that is a reason why you can use them both.

If you use them both, [Cache-Control] has priority. More information you can find here: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9.3