title: What's the difference between expires, max-age, and shared max-age?
body: <p>I have never used <strong>HTTP Caching</strong>.</p>
  
  <p>I found those caching options on <a href="http://symfony.com/doc/2.0/bundles/SensioFrameworkExtraBundle/annotations/cache.html" rel="noreferrer">Symfony documentation page</a>.</p>
  
  <p>I just wanted to know what's the difference between <code>expires</code>, <code>max-age</code>, and <code>s-maxage</code> headers?</p>