PX_IUnknown
Visual Studio 2010
Call this function within your control's DoPropExchange member function to serialize or initialize a property represented by an object having an IUnknown-derived interface.
BOOL PX_IUnknown( CPropExchange* pPX, LPCTSTR pszPropName, LPUNKNOWN& pUnk, REFIID iid, LPUNKNOWN pUnkDefault = NULL );