Countable
Though not strictly part of the Iterator design pattern (and definitely distinct from the Iterator interface of the SPL Library), implementing the Countable interface is complementary functionality.
Iterator Design Pattern
The Iterator design pattern is used to elegantly retrieve the members of a collection. In PHP 5, that means implementing the Iterator interface defined in the Standard PHP Library (SPL).
Front Controller Design Pattern
One way to more efficiently and securely manage a web application is to implement the Front Controller design pattern. This pattern calls for a single object to route web traffic: This means there must be an entry point (commonly called the bootstrap) where the application defers control to the Front Controller object.