code: def S(self):
  		
  		
  		if self._combining:
  			raise TypeError("Unable to dereference after combining fields.")
  		
  		instance = self.__class__(self._document, self._field)
  		instance._name = self._name + '.' + '$'  # pylint:disable=protected-access
  		return instance
docs: Allow for the projection (and update) of nested values contained within the single match of an array.
  		
  		Projection operator: https://docs.mongodb.com/manual/reference/operator/projection/positional/#proj._S_
  		Array update operator: https://docs.mongodb.com/manual/reference/operator/update/positional/