code: public function getIterator(IteratorFilter $itf = null)
      {
          if (is_null($itf)) {
              return new AnyIterator($this->collection);
          }
  
          return new AnyIterator($itf->match($this->collection));
      }
docs: Get an Iterator filtered by an IteratorFilter
  @param IteratorFilter $itf
  @return GenericIterator