code: public static boolean isInterElementWhitespace(String text) {
      int n = text.length();
      for (int i = 0; i < n; ++i) {
        if (!Strings.isHtmlSpace(text.charAt(i))) {
          return false;
        }
      }
      return true;
    }
docs: True if text is the value of an inter-element whitespace text node as
  defined by HTML5.
  <p>
  This is the kind of text that is often inserted by
  HTML authors to nicely indent their HTML documents and which
  (modulo unconventional use of {@code white-space:pre}) are not apparent
  to the end-user.