docs: def generate_xhtml(path, dirs, files):
      """Return a XHTML document listing the directories and files."""
      # Prepare the path to display.
      if path != '/':
          dirs.insert(0, '..')
      if not path.endswith('/'):
          path += '/'
  
      def itemize(item):
          return '<a href="%s">%s</a>' % (item, path+item)
      dirs = [d + '/' for d in dirs]
      return """
      <html>
       <body>
        <h1>%s</h1>
         <pre>%s\n%s</pre>
       </body>
      </html>
      """ % (path, '\n'.join(itemize(dir) for dir in dirs), '\n'.join(itemize(file) for file in files))