docs: def tt2nav(toctree, klass=None, appendix=None, divider=False):
      """
      Injects ``has-dropdown`` and ``dropdown`` classes to HTML
      generated by the :func:`toctree` function.
      
      :param str toctree:
          HTML generated by the :func:`toctree` function.
      """
      
      tt = toctree
      divider = '<li class="divider"></li>' if divider else ''
      
      # Append anything just before the closing </ul>.
      if appendix:
          tt = re.sub(r'(</ul>$)', r'{}\1'.format(appendix), tt)
      
      # Add class attribute to all <ul> elements.
      tt = re.sub(r'<ul>', r'<ul class="">', tt)
      
      # Add class to first <ul> tag.
      if klass:
          tt = re.sub(r'(^<ul[\s\w-]+class=")', r'\1{} '.format(klass), tt)
      
      # Add class "active" to all <li> tags with "current" class.
  #    tt = re.sub(r'(<li[\s\w-]+class="[^"]*current)([^"]*")', r'\1 active\2', tt)
      
      # Match each <li> that contains <ul>.
      pattern = r'(<li[\s\w-]+class=")([^>]*>[^<]*<a[^>]*>[^<]*</a>[^<]*<ul[\s\w]+class=")'
      
      # Inject the classes.
      replace = r'{}\1has-dropdown \2dropdown '.format(divider)
      
      # Do the replace and return.
      return re.sub(pattern, replace, tt)