code: public void setUrl(String url) {
          if (url != null && url.trim().length() > 0) {
              if (Url.isUrl(url)) {
                  this.url = url;
              } else {
                  throw new IllegalArgumentException(url + " is not a valid URL.");
              }
          }
      }
docs: Sets the URL where more information about this element can be found.
  
  @param url   the URL as a String
  @throws IllegalArgumentException     if the URL is not a well-formed URL