code: public void pushUlterior(String key, Object value) {
          assertArgumentNotNull("key", key);
          assertArgumentNotNull("value", value);
          postcard.pushUlterior(key, value);
      }
docs: Push element of ulterior parameter. <br>
  Basically unused in mailflute, this is for extension by application.
  @param key The key of the element. (NotNull)
  @param value The value of the element. (NotNull)