public void actionOpenFile()
   {
      JFileChooser fc = new JFileChooser();
      fc.setFileSelectionMode(JFileChooser.FILES_ONLY);
      fc.setDialogTitle(UIStrings.UI_OPEN_MDFILE_LABEL);
      fc.addChoosableFileFilter(new FileNameExtensionFilter(
              "Markdown files (.md, .mmd, .markdown, .txt, .text)", "md", "mmd", "markdown", "txt", "text"));
      int returnVal = fc.showOpenDialog(Joculus.frame);

      if (returnVal == JFileChooser.APPROVE_OPTION)
      {
         File file = fc.getSelectedFile();
         if (file.exists() && file.isFile())
         {
            app_instance.setFile(file.getAbsolutePath());
         }
      }
   }