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

14.29 Last-ModifiedThe Last-Modified entity-header field indicates the date and time atwhich the origin server believes the variant was last modified.Last-Modified = "Last-Modified" ":" HTTP-dateFielding, et al. Standards Track [Page 134]RFC 2616 HTTP/1.1 June 1999An example of its use isLast-Modified: Tue, 15 Nov 1994 12:45:26 GMTThe exact meaning of this header field depends on the implementationof the origin server and the nature of the original resource. Forfiles, it may be just the file system last-modified time. Forentities with dynamically included parts, it may be the most recentof the set of last-modify times for its component parts. For databasegateways, it may be the last-update time stamp of the record. Forvirtual objects, it may be the last time the internal state changed.An origin server MUST NOT send a Last-Modified date which is laterthan the server's time of message origination. In such cases, wherethe resource's last modification would indicate some time in thefuture, the server MUST replace that date with the messageorigination date.An origin server SHOULD obtain the Last-Modified value of the entityas close as possible to the time that it generates the Date value ofits response. This allows a recipient to make an accurate assessmentof the entity's modification time, especially if the entity changesnear the time that the response is generated.HTTP/1.1 servers SHOULD send Last-Modified whenever feasible.14.30 LocationThe Location response-header field is used to redirect the recipientto a location other than the Request-URI for completion of therequest or identification of a new resource. For 201 (Created)responses, the Location is that of the new resource which was createdby the request. For 3xx responses, the location SHOULD indicate theserver's preferred URI for automatic redirection to the resource. Thefield value consists of a single absolute URI.Location= "Location" ":" absoluteURI