The Traversable interface
(PHP 5 >= 5.0.0)
Interface to detect if a class is traversable using foreach.
This is an internal engine interface which cannot be implemented in PHP scripts. Either IteratorAggregate or Iterator must be used instead. When implementing an interface which extends Traversable, make sure to list IteratorAggregate or Iterator before its name in the implements clause.
This interface has no methods, its only purpose is to be the base interface for all traversable classes.