docs: def expand_env_lazy(loader, node):
      """
      Substitutes a variable read from a YAML node with the value stored in Fabric's ``env`` dictionary. Creates an
      object for late resolution.
  
      :param loader: YAML loader.
      :type loader: yaml.loader.SafeLoader
      :param node: Document node.
      :type node: ScalarNode
      :return: Corresponding value stored in the ``env`` dictionary.
      :rtype: any
      """
      val = loader.construct_scalar(node)
      return lazy_once(env_get, val)