(PHP 5 >= 5.3.0)
An Iterator that sequentially iterates over all attached iterators
$flags
     = MultipleIterator::MIT_NEED_ALL|MultipleIterator::MIT_KEYS_NUMERIC
   
  ] )MultipleIterator::MIT_NEED_ANY
     Do not require all sub iterators to be valid in iteration.
MultipleIterator::MIT_NEED_ALL
     Require all sub iterators to be valid in iteration.
MultipleIterator::MIT_KEYS_NUMERIC
     Keys are created from the sub iterators position.
MultipleIterator::MIT_KEYS_ASSOC
     Keys are created from sub iterators associated information.