def xml(t, tag = nil)
      if tag
        t.__send__(tag, "xsi:type" => "AdGroupAd") { |t| _xml(t) }
      else
        _xml(t)
      end
    end
def xml(t, tag = nil)
      if tag
        t.__send__(tag, "xsi:type" => "AdGroupAd") { |t| _xml(t) }
      else
        _xml(t)
      end
    end
Marshall with Builder::XmlMarkup