code: public SafeHtmlBuilder appendContent(Iterator<SafeHtml> htmls) {
      checkNotVoidElement();
      while (htmls.hasNext()) {
        contents.add(htmls.next());
      }
      return this;
    }
docs: Appends the given {@code htmls} as this element's content, in the sequence the Iterator returns
  them.
  
  @throws IllegalStateException if this builder represents a void element