Fixed #20459 - Improved example for setting HTTP header fields.

Thanks Jérémie Blaser.

AUTHORS

@@ -111,6 +111,7 @@ answer newbie questions, and generally made Django that much better:
     Paul Bissex <http://e-scribe.com/>
     Loïc Bistuer <loic.bistuer@sixmedia.com>
     Simon Blanchard
+    Jérémie Blaser <blaserje@gmail.com>
     Craig Blaszczyk <masterjakul@gmail.com>
     David Blewett <david@dawninglight.net>
     Artem Gnilov <boobsd@gmail.com>

docs/ref/request-response.txt

@@ -584,12 +584,19 @@ Setting header fields
 To set or remove a header field in your response, treat it like a dictionary::
 
     >>> response = HttpResponse()
-    >>> response['Cache-Control'] = 'no-cache'
-    >>> del response['Cache-Control']
+    >>> response['Age'] = 120
+    >>> del response['Age']
 
 Note that unlike a dictionary, ``del`` doesn't raise ``KeyError`` if the header
 field doesn't exist.
 
+For setting the ``Cache-Control`` and ``Vary`` header fields, it is recommended
+to use the :meth:`~django.utils.cache.patch_cache_control` and
+:meth:`~django.utils.cache.patch_vary_headers` methods from
+:mod:`django.utils.cache`, since these fields can have multiple, comma-separated
+values. The "patch" methods ensure that other values, e.g. added by a
+middleware, are not removed.
+
 HTTP header fields cannot contain newlines. An attempt to set a header field
 containing a newline character (CR or LF) will raise ``BadHeaderError``