title: Accept-Datetime header field in HTTP
body: <p>I found on wikipedia that <a href="http://en.wikipedia.org/wiki/List_of_HTTP_header_fields#Request_fields" rel="nofollow">Accept-Datetime header field</a>  is "Acceptable version in time".</p>
  
  <p>It isn't really clear to me what is the meaning of that field and what does it really provide?</p>