[Zope] Content-type

Hi, I am a little confused with how to set the Content-type of the method or document that is being served by zope. I would like to be able to set it to multipart/x-mixed-replace so that I can do some server-push. I have tried the following without success. <dtml-call "REQUEST['RESPONSE'].setHeader('CONTENT_TYPE','multipart/x-mixed-replace')"> <dtml-var "REQUEST['RESPONSE'].setHeader('CONTENT_TYPE','multipart/x-mixed-replace')"> When I do a <dtml-var "REQUEST['RESPONSE'].getHeader('CONTENT_TYPE')"> I just get 'NONE' terry