code: private String getOutputFileExtension ()
    {
      if (Boolean.TRUE.equals (this.text) || Boolean.TRUE.equals (this.bnf))
      {
        return ".txt";
      }
      else
      {
        return ".html";
      }
    }
docs: The JJDoc output file will have a <code>.html</code> or <code>.txt</code>
  extension depending on the value of the parameters {@link #text} and
  {@link #bnf}.
  
  @return The file extension (including the leading period) to be used for
  the JJDoc output files.