(PHP 5 >= 5.1.0, PHP 7, PHP 8)
IteratorIterator::valid — Проверяет, допустим ли текущий элемент
Метод проверяет, допустим ли текущий элемент.
Сигнатура функции не содержит параметров.
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()