SPL provides a set of iterators to traverse over objects.
  
  
   Undocumented Iterators
   
    - AppendIterator
- EmptyIterator
- InfiniteIterator
- MultipleIterator
- NoRewindIterator
- RecursiveArrayIterator
- RecursiveFilterIterator
- RecursiveRegexIterator
- RecursiveTreeIterator
- RegexIterator