(PHP 5 >= 5.3.0, PHP 7)
MultipleIterator::key — Gets the registered iterator instances
Get the registered iterator instances key() result.
This function is currently not documented; only its argument list is available.
This function has no parameters.
An array of all registered iterator instances,
or FALSE if no sub iterator is attached.
A LogicException if mode MIT_NEED_ALL is set,
and at least one attached iterator is not valid.
Calling this method from foreach triggers warning "Illegal type returned".