HTTP cache control response headers

http://www.mnot.net/cache_docs/

http://code.google.com/speed/page-speed/docs/caching.html

Expires        --\
                  |-->  Or  --\
Cache-Control  --/             \
                                |-->  And
Last-Modified  --\             /
                  |-->  Or  --/
Etag           --/

• The headers placed under [Or] classification: Only one of them need to be added. Adding both is just redundant information.
• Expires and Last-Modified were introduced in HTTP 1.0 specification.
• Cache-Control and Etag were introduced in HTTP 1.1 specification.

Cache-Control max-age value

http://www.web-caching.com/mnot_tutorial/how.html

The max-age value in Cache-Control header represents in seconds the freshness of the resource from the time of request.

Cache-Control value examples:

• no-cache
• For 1 day:
  max-age=86400
• For 31 days:
  max-age=2678400
• For 365 days:
  max-age=31536000