code: def get_last_array(self):
          
          # Get the root array (might not have been registered).
          root = self.repo[self.id]
  
          # Get length and last item in the root array.
          apex_id, apex_height = root.get_last_item_and_next_position()
  
          # Bail if there isn't anything yet.
          if apex_id is None:
              return None, None
  
          # Get the current apex array.
          apex = self.repo[apex_id]
          assert isinstance(apex, Array)
  
          # Descend until hitting the bottom.
          array = apex
          array_i = 0
          height = apex_height
          while height > 1:
              height -= 1
              array_id, width = array.get_last_item_and_next_position()
              assert width > 0
              offset = width - 1
              array_i += offset * self.repo.array_size ** height
              array = self.repo[array_id]
  
          return array, array_i
docs: Returns last array in compound.
  
          :rtype: CompoundSequenceReader