A singleton is an object class designed such that only one instance of that class will ever exist. This can be useful to minimize resources required (e.g., database connections) or ensure consistent data throughout an application (e.g., user preferences).
A term first introduced by Martin Fowler and Eric Evans, a fluent interface is one in which a class is self-referencial wherever possible, resulting in cleaner code. Wherever possible, the Istarel Workshop Application Framework utilizes fluent interfaces.
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).