title: No expires header sent, content cached, how long until browser makes conditional GET request?
body: <p>Assume browser default settings, and content is sent without expires headers. </p>
  
  <ol>
  <li>user visits website, browser caches images etc. </li>
  <li>user does not close browser, or refresh page. </li>
  <li>user continues to surf site normally.</li>
  <li>assume the browse doesn't dump the cache for any reason. </li>
  </ol>
  
  <p>The browser will cache images etc as the user surfs, but it's unclear when it will issue a conditional GET request to ask about content freshness (apart from refreshing the page). If this is a browser specific setting, where can I see it's value (for browsers like: safari, IE, FireFox, Chrome). </p>
  
  <p>[edit: yes - I understand that you should always send expires headers. However, this research is aimed at understanding how the browser works with content w/o expires headers.]</p>