Clarify the possibility to lose the array pointer with next() and prev()

From manual page: https://php.net/function.next

If the next or prev function goes beyond the array, it is not possible to return to the previous (first/last element)!

// example
$array = array(
    'fruit1' => 'apple',
    'fruit2' => 'orange',
    'fruit3' => 'grape',
    'fruit4' => 'apple',
    'fruit5' => 'apple');

reset($array); // prepare array

$row = current($array);
var_dump($row); // 'apple'

$row = prev($array);
var_dump($row); // false

$row = next($array); // it is not possible to return to the previous (first/last element)!
var_dump($row); // false

Start with the PHP manual page for next(), linked in the issue, and review the related prev() behavior and example. Update the documentation so the pointer behavior and the intended outcome of the example are unambiguous, then verify that the revised wording matches the manual's conventions.