Use between the BEGIN_CONNECTION_PART and END_CONNECTION_PART macros to define an interface ID for a connection point supported by your OLE control.
The interface ID of the interface called by the connection point.
The iid argument is an interface ID used to identify the interface that the connection point will call on its connected sinks. For example:
CONNECTION_IID( IID_IsinkInterface )
specifies a connection point that calls the ISinkInterface interface.