code: @TCB
    static String stripBannedCodeunits(String s) {
      int safeLimit = longestPrefixOfGoodCodeunits(s);
      if (safeLimit < 0) { return s; }
  
      StringBuilder sb = new StringBuilder(s);
      stripBannedCodeunits(sb, safeLimit);
      return sb.toString();
    }
docs: Returns the portion of its input that consists of XML safe chars.
  @see <a href="http://www.w3.org/TR/2008/REC-xml-20081126/#charsets">XML Ch. 2.2 - Characters</a>