Object Extensions for PHP: Extend objects with more functions and variables

Object Extensions for PHP
A runtime object extension and callback library for PHP

The Object Extensions library for PHP adds the following functionality
to objects that extend the base class:

 - Runtime object extension to "extend" an object by another class at
   runtime (to virtually inherit all public properties and methods).
 - Runtime callback definitions to be able to pass function/method
   callbacks as variables, and subsequently execute them from other
   function/methods.
 - Dynamic object properties class to handle runtime setting/getting
   of object properties, as well as ability to pass function arguments
   as object-based parameters rather than long list of options.

OBJECT EXTENSION:

 - Base class (CExtendable) implements a _extend() function by which
   you may vritually extend an object by an instance of another object.
 - Extended object (object passed to _extend) can reference parent
   object if supported by extended class.
 - __get, __set and __call are all overriden to handle overriding
   undefined properties and methods
 - Ability to reference a callback in a straightforward manner
   ($object->_callback()->method(args, [...]))

CALLBACK FUNCTIONALITY:

 - Can create callbacks directly (through CCallback and derived
   classes)
 - Can create method callbacks by calling _callback() method on
   CExtendable objects
 - When combined with object extension and object properties, can
   provide a really easy way to execute callbacks.

OBJECT PROPERTIES:

 - Base class extends ArrayIterator, all properties saved in an array
 - Basic functionality to check values provided and/or set default
   values.
 - Overrides __get, __set to get/set object properties.
 - Can limit property set-tability to existing properties only, or to
   provided array of properties.
 - Can enable read-only mode.
 - Overrides __call, and in the case that the a property value with
   the same name as the method name exists, and is an instance of the
   ICallback interface, this callback is executed.

PHP COMPATIBILITY:

Object Extensions for PHP uses PHP5 functionality.  It would be
theoretically possible to implement similar functionality into PHP4,
however, since I no longer develop in PHP4, I cannot properly test it.