(PHP 5 >= 5.1.0, PHP 7) Move to next element

(PHP 5 >= 5.1.0, PHP 7) Rewind to the first element

(PHP 5 >= 5.1.0, PHP 7) Checks whether the current element has sub elements.

(PHP 5 >= 5.1.0, PHP 7) Check whether the current element is valid

(PHP 5 >= 5.1.0, PHP 7) Returns the sub-elements of the current element

(PHP 5 >= 5.1.0, PHP 7) Returns the current element

(PHP 5 >= 5.1.0, PHP 7) Return current key