code: public String html() {
          StringBuilder accum = StringUtil.borrowBuilder();
          html(accum);
          String html = StringUtil.releaseBuilder(accum);
          return NodeUtils.outputSettings(this).prettyPrint() ? html.trim() : html;
      }
docs: Retrieves the element's inner HTML. E.g. on a {@code <div>} with one empty {@code <p>}, would return
  {@code <p></p>}. (Whereas {@link #outerHtml()} would return {@code <div><p></p></div>}.)
  
  @return String of HTML.
  @see #outerHtml()