title: How necessary it is to use "must-revalidate" in "Cache-Control: no-cache, must-revalidate"
body: <p>Often I use</p>
  
  <pre><code>Cache-Control: no-cache
  </code></pre>
  
  <p>or </p>
  
  <pre><code>Cache-Control: max-age=0
  </code></pre>
  
  <p>The spec says <code>must-revalidate</code> is for <code>max-stale</code>... (the server issue <code>max-stale</code>?)</p>
  
  <p>So if for normal web servers, Apache, or Rails with Mongrels, then I think usually there is no <code>max-stale</code>, so <code>must-revalidate</code> is not needed?</p>