code: def of_type(self, *kinds):
  		
  		
  		if self._combining:  # We are a field-compound query fragment, e.g. (Foo.bar & Foo.baz).
  			return reduce(self._combining, (q.of_type(*kinds) for q in self._field))
  		
  		foreign = set(kinds) if kinds else self._field.__foreign__
  		
  		if not foreign:
  			return Filter()
  		
  		if len(foreign) == 1:  # Simplify if the value is singular.
  			foreign, = foreign  # Unpack.
  		
  		return Filter({self._name: {'$type': foreign}})
docs: Selects documents if a field is of the correct type.
  		
  			Document.field.of_type()
  			Document.field.of_type('string')
  		
  		Element operator: {$type: self.__foreign__}
  		Documentation: https://docs.mongodb.org/manual/reference/operator/query/type/#op._S_type