(PHP 5 >= 5.1.0, PHP 7, PHP 8)
IteratorIterator::valid — Verifica si el elemento actual es válido
Verifica si el elemento actual es válido.
Esta función no contiene ningún parámetro.
An Iterator is "valid" when it has additional elements, beyond its element index.
Said another way: After an Iterator is next()'d to its final element, the Iterator is no longer "valid".
Said another way: A "hasNext" check would simply return ::valid()