The SetHeader method will change the value of a response header for the specified client session, 
          typically within an OnCommand event handler. If the 
          HeaderName value matches an existing header field, its value 
          will be replaced. If the header name is not defined, then a new header 
          will be created with the given value. You should not change the value 
          of most standard response header values 
          unless you are certain of the impact that it would have on the normal 
          operation of the client.
          If you wish to define a custom header value that would be included 
          in the response to a client request, you should prefix the header name 
          with "X-" to avoid potential conflicts with the standard response 
          headers. For example, if you wanted to identify a customer, you could 
          create a header field with the name "X-Customer-ID" and set the value 
          to the customer ID number. The client application would receive this 
          custom header value as part of the response to its request for a 
          document.
          
          Refer to Hypertext
          Transfer Protocol Headers for a list of common request and response
          headers that are used.