--- a/http.rst	Fri Nov 12 21:47:05 2010 +0200
+++ b/http.rst	Fri Nov 12 21:51:53 2010 +0200
@@ -14,3 +14,23 @@
 
   Content-Encoding: gzip
 
+* ETags.
+
+Server respond:
+
+  HTTP/1.1 200 OK
+  Last-Modified: Tue, 12 Dec 2006 03:03:59 GMT
+  ETag: "10c24bc-4ab-457e1c1f"
+  Content-Length: 12195
+
+Lately client send:
+
+  GET /i/yahoo.gif HTTP/1.1
+  Host: us.yimg.com
+  If-Modified-Since: Tue, 12 Dec 2006 03:03:59 GMT
+  If-None-Match: "10c24bc-4ab-457e1c1f"
+
+and get respond:
+
+  HTTP/1.1 304 Not Modified
+