title: Correct behavior with If-Match the header?
body: <p>According to <a href="http://www.ietf.org/rfc/rfc2616.txt" rel="noreferrer">RFC 2616</a>, generation of entity tags by HTTP servers is optional. However, I couldn't find what a <em>conditionally</em> compliant HTTP server should do if it receives an <code>If-Match</code> (or <code>If-None-Match</code>) header. Should it just ignore those headers or should it respond with <code>412 Precondition Failed</code>?  </p>
  
  <p>UPD: Just to clarify, I'm assuming that the server in question does not support entity tags.</p>