The PHP.cc have posted another article in their series looking at the new features that come with the latest release of PHP (5.5). In this new post they cover the "CLASS" constant.

Last week, the first stable version of PHP 5.5 was released. It introduced a class-level constant, aptly named CLASS, that is automatically available on all classes and holds the fully-qualified name of that class. [...] So why would you need such a constant? [...] When you need the fully qualified name of a namespaced class that is referenced by a namespace alias ... then it gets interesting.

He illustrates with an example of a unit test using stubs and mocks. The normal method requires the definition of the class namespace in the "getMock" call. With the CLASS constant, PHP can extract that information from the namespace referenced in the "use" and drop it in as a replacement.