When writing a plug-in that derives from a base class, 3ds Max will expose much of the necessary functionality through the arguments to the virtual functions that you override. In cases where you need access to additional functionality provided by 3ds Max the global function GetCOREInterface14() can be very useful. This function returns a pointer to a global object of type Interface14, which provides access to much of the core functionality of 3ds Max.
GetCOREInterface() which returns a pointer to an Interface object. Interface14 derives from Interface but provides additional functionality.