Certain packages consist of multiple classes that are used in cooperation. Such classes usually need to access each other protected variables or functions.
In other languages there are friend classes like in C++ or package classes like in Java that allow restricting the access to variables of functions to cooperating classes.
Even with the enhancements of version 5 object model, there is no PHP support to this concept similar to C++ friend or Java package classes.
This class provides an emulation of such concept that works under PHP 5.