title: What requests do browsers' "F5" and "Ctrl + F5" refreshes generate?
body: <p>Is there a standard for what actions <kbd>F5</kbd> and <kbd>Ctrl</kbd>+<kbd>F5</kbd> trigger in web browsers?</p>
  <p>I once did experiment in IE6 and Firefox 2.x. The <kbd>F5</kbd>  refresh would trigger a HTTP request sent to the server with an <code>If-Modified-Since</code> header, while <kbd>Ctrl</kbd>+<kbd>F5</kbd> would not have such a header. In my understanding, <kbd>F5</kbd>  will try to utilize cached content as much as possible, while <kbd>Ctrl</kbd>+<kbd>F5</kbd> is intended to abandon all cached content and just retrieve all content from the servers again.</p>
  <p>But today, I noticed that in some of the latest browsers (Chrome, IE8) it doesn't work in this way anymore. Both <kbd>F5</kbd> and <kbd>Ctrl</kbd>+<kbd>F5</kbd> send the <code>If-Modified-Since</code> header.</p>
  <p>So how is this supposed to work, or (if there is no standard) how do the major browsers differ in how they implement these refresh features?</p>