title: no 'Last-Modified' HTTP header -> however cached?
body: <p>From a browser perspective,</p>
  
  <p>What occur if a component (image, script, stylesheet...) is served without a <code>Last-Modified</code> HTTP header field...</p>
  
  <p>Is it however cached by the browser even if it won't be able to perform a validity check(<code>If-Modified-Since</code>) in future, due to his lack of date/time information?</p>
  
  <p>Eg:</p>
  
  <pre><code>GET /foo.png HTTP/1.1
  Host: example.org
  --
  200 OK
  Content-Type: image/png
  
  ...
  </code></pre>
  
  <p>Is <code>foo.png</code> however cached?</p>
  
  <p>--</p>
  
  <p>Would you know any online service to serve my raw HTTP response that I can write myself in order to test what I'm asking ?</p>
  
  <p>Thank you.</p>