Network Working Group R. Fielding Request for Comments: 2616 ...

Content) instead of 200 (OK).- The presence of a Range header in a conditional GET (a requestusing one or both of If-Modified-Since and If-None-Match, orone or both of If-Unmodified-Since and If-Match) modifies whatis returned if the GET is otherwise successful and thecondition is true. It does not affect the 304 (Not Modified)response returned if the conditional is false.In some cases, it might be more appropriate to use the If-Rangeheader (see section 14.27) in addition to the Range header.If a proxy that supports ranges receives a Range request, forwardsthe request to an inbound server, and receives an entire entity inreply, it SHOULD only return the requested range to its client. ItSHOULD store the entire received response in its cache if that isconsistent with its cache allocation policies.14.36 RefererThe Referer[sic] request-header field allows the client to specify,for the server's benefit, the address (URI) of the resource fromwhich the Request-URI was obtained (the "referrer", although theheader field is misspelled.) The Referer request-header allows aserver to generate lists of back-links to resources for interest,logging, optimized caching, etc. It also allows obsolete or mistypedlinks to be traced for maintenance. The Referer field MUST NOT besent if the Request-URI was obtained from a source that does not haveits own URI, such as input from the user keyboard.Referer = "Referer" ":" ( absoluteURI | relativeURI )Example:Referer: http://www.w3.org/hypertext/DataSources/Overview.htmlFielding, et al. Standards Track [Page 140]RFC 2616 HTTP/1.1 June 1999If the field value is a relative URI, it SHOULD be interpretedrelative to the Request-URI. The URI MUST NOT include a fragment. Seesection 15.1.3 for security considerations.14.37 Retry-AfterThe Retry-After response-header field can be used with a 503 (Service