title: HTTP If-None-Match vs. If-Match
body: <p>I'm currently building up a PHP script that will answer HTTP "304 Not Modified" when required.</p>
  
  <p>(See <a href="https://stackoverflow.com/questions/2086712/http-if-none-match-and-if-modified-since-and-304-clarification-in-php">question #2086712</a> for what I do so far).</p>
  
  <p>Currently I answer to the following:</p>
  
  <ul>
  <li>If-Modified-Since</li>
  <li>If-None-Match</li>
  </ul>
  
  <p>But I found out that 3 more headers can trigger a "conditional GET" (See <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.3" rel="noreferrer">http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.3</a>):</p>
  
  <ul>
  <li>If-Match</li>
  <li>If-Unmodified-Since</li>
  <li>If-Range</li>
  </ul>
  
  <p>The last 2 seems irrevelent to my caching system (they seem to be used when resuming "big" downloads) but I haven't found if "If-Match" could be of use in my system.</p>
  
  <p>Does "If-Match" is used in proxies or Web browser for "regular" page content? How "If-Match" is different than "If-None-Match"?</p>
  
  <p>Should I support those 3 or just some of them? Any help welcome!</p>