docs: def aggregate(self, mapped_coll_generator, coll_type, visitor):
          """Hook called for each normalize.coll.Collection, after mapping over
          each of the items in the collection.
  
          The default implementation calls
          :py:meth:`normalize.coll.Collection.tuples_to_coll` with
          ``coerce=False``, which just re-assembles the collection into a native
          python collection type of the same type of the input collection.
  
          args:
  
              ``result_coll_generator=`` *generator func*
                  Generator which returns (key, value) pairs (like
                  :py:meth:`normalize.coll.Collection.itertuples`)
  
              ``coll_type=``\ *CollectionType*
                  This is the :py:class:`normalize.coll.Collection`-derived
                  *class* which is currently being reduced.
  
              ``visitor=``\ *Visitor*
                  Context/options object
          """
          return coll_type.tuples_to_coll(mapped_coll_generator, coerce=False)