The function pool is generic. Its purpose is to combine
  data from several objects of the same type (typically computed
  from different datasets) into a common, pooled estimate.
The function pool.anyist is the method
  for the class "anylist". It is used when the objects to be
  pooled are given in a list x.
Each of the elements of the list x, and each of the
  subsequent arguments … if provided, must be an object of the same
  class.