(PHP 5 >= 5.1.0, PHP 7) Validates the iterator
(PHP 5 >= 5.1.0, PHP 7) Forward to the next element
(PHP 5 >= 5.1.0, PHP 7) Prevents the rewind operation on the inner iterator.
(PHP 5 >= 5.1.0, PHP 7) Get the current value
(PHP 5 >= 5.1.0, PHP 7) Construct a NoRewindIterator
(PHP 5 >= 5.1.0, PHP 7) Get the inner iterator
(PHP 5 >= 5.1.0, PHP 7) Get the current key