code: public static SafeHtml concat(Iterable<SafeHtml> htmls) {
      int concatLength = 0;
      for (SafeHtml html : htmls) {
        concatLength += html.getSafeHtmlString().length();
      }
  
      StringBuilder result = new StringBuilder(concatLength);
      for (SafeHtml html : htmls) {
        result.append(html.getSafeHtmlString());
      }
      return create(result.toString());
    }
docs: Creates a new SafeHtml which contains, in order, the string representations of the given
  {@code htmls}.