public void setValidUntil(String validUntil)
   {
      if (validUntil == null || validUntil.length() != 8 || !validUntil.matches("\\d{8}"))
         throw new IllegalArgumentException("The valid until date field in the " + frameType.getId() + " frame contains an invalid value, " + validUntil  + ".  It must have the format YYYYMMDD.");

      this.dirty      = true;
      this.validUntil = validUntil;
   }