This method has no unique definition. Generally speaking, methods which always return the same type usually don’t use #class, but #species. For example, a PositionableStream’s species is the class of the collection on which it is streaming (used by upTo:, upToAll:, upToEnd). Stream uses species for obtaining the class of next:’s return value, Collection uses it in its #copyEmpty: message, which in turn is used by all collection-returning methods. An Interval’s species is Array (used by collect:, select:, reject:, etc.).
Answer the receiver