* called by the {@link #escape(String)} method when it discovers that escaping is required. It is
   * protected to allow subclasses to override the fastpath escaping function to inline their
   * escaping test. See {@link CharEscaperBuilder} for an example usage.
   *
   * <p>This method is not reentrant and may only be invoked by the top level {@link
   * #escape(String)} method.
   *
   * @param s the literal string to be escaped