Definition
Observable defines Visitor
// Differs from Mapper only in return type, since this callback is exclusively
// used to visit each element in a sequence, not transform it.
callback Visitor = undefined (any value, unsigned long long index);Visitor callbackObservable defines Visitor
// Differs from Mapper only in return type, since this callback is exclusively
// used to visit each element in a sequence, not transform it.
callback Visitor = undefined (any value, unsigned long long index);