[Zope] How to set an Expires header?

[skip@calendar.com (Skip Montanaro)]

I have a search function that sets the expires header of the RESPONSE:

  def search(RESPONSE, performers=None, keywords=None, venue="", event="",
	     city="", state="", country="", date="", age=10000, radius=0,
	     repeat="once", format="text", editor="", email="",
	     start=0, nhits=20, REQUEST=None):
      """Musi-Cal search function"""

      ...

      RESPONSE.setHeader('Expires', time.strftime("%a, %d %b %Y %H:%M:%S GMT",
						  time.gmtime(time.time())))
      return _search_tmpl(...,
			  REQUEST=REQUEST,
			  RESPONSE=RESPONSE,
			  ...)

but I don't see any expires header in the response:

    HTTP/1.0 200 OK
    Server: Medusa/1.4
    Content-Length: 30605
    Date: Mon, 01 Feb 1999 21:46:55 GMT

Am I doing something wrong or am I encountering a wart on ZServer?  I
haven't tried ZopeHTTPServer, but that will be my step.

Skip Montanaro	| Mojam: "Uniting the World of Music" http://www.mojam.com/
skip@mojam.com  | Musi-Cal: http://www.musi-cal.com/
518-372-5583