docs: def adapt_package(package):
      """Adapts ``.epub.Package`` to a ``BinderItem`` and cascades
      the adaptation downward to ``DocumentItem``
      and ``ResourceItem``.
      The results of this process provide the same interface as
      ``.models.Binder``, ``.models.Document`` and ``.models.Resource``.
      """
      navigation_item = package.navigation
      html = etree.parse(navigation_item.data)
      tree = parse_navigation_html_to_tree(html, navigation_item.name)
      return _node_to_model(tree, package)