docs: def extras(request):
      """Return a dict with archive metadata for webview."""
      key = request.matchdict.get('key', '').lstrip('/')
      key_map = {
          'languages': _get_available_languages_and_count,
          'subjects': _get_subject_list,
          'featured': _get_featured_links,
          'messages': _get_service_state_messages,
          'licenses': _get_licenses
          }
  
      with db_connect() as db_connection:
          with db_connection.cursor() as cursor:
              if key:
                  proc = key_map[key]
                  metadata = {key: proc(cursor)}
              else:
                  metadata = {key: proc(cursor)
                              for (key, proc) in key_map.items()}
  
      resp = request.response
      resp.status = '200 OK'
      resp.content_type = 'application/json'
      resp.body = json.dumps(metadata)
      return resp