# File lib/mechanize/chain/custom_headers.rb, line 6
      def handle(ctx, params)
        request = params[:request]
        params[:headers].each do |k,v|
          case k
          when :etag then request["ETag"] = v
          when :if_modified_since then request["If-Modified-Since"] = v
          else
            raise ArgumentError.new("unknown header symbol #{k}") if k.is_a? Symbol
            request[k] = v
          end
        end
        super
      end