code: public void title(String title) {
          Validate.notNull(title);
          Element titleEl = getElementsByTag("title").first();
          if (titleEl == null) { // add to head
              head().appendElement("title").text(title);
          } else {
              titleEl.text(title);
          }
      }
docs: Set the document's {@code title} element. Updates the existing element, or adds {@code title} to {@code head} if
  not present
  @param title string to set as title