Understanding COM Event Handling

// EventFiringObject.idl : IDL source for EventFiringObject.dll
//

// This file will be processed by the MIDL tool to
// produce the type library (EventFiringObject.tlb) and marshalling code.

import "oaidl.idl";
import "ocidl.idl";
	[
		object,
		uuid(8E396CC0-A266-481E-B6B4-0CB564DAA3BC),
		dual,
		helpstring("IEventFiringObject Interface"),
		pointer_default(unique)
	]
	interface IEventFiringObject : IDispatch
	{
		[id(1), helpstring("method TestFunction")] HRESULT TestFunction([in] long lValue);
	};

[
	uuid(0B199966-76EA-479F-881D-ED7CB5F3457B),
	version(1.0),
	helpstring("EventFiringObject 1.0 Type Library")
]
library EVENTFIRINGOBJECTLib
{
	importlib("stdole32.tlb");
	importlib("stdole2.tlb");

	[
		uuid(32F2B52C-1C07-43BC-879B-04C70A7FA148),
		helpstring("_IEventFiringObjectEvents Interface")
	]
	dispinterface _IEventFiringObjectEvents
	{
		properties:
		methods:
		[id(1), helpstring("method Event1")] HRESULT Event1([in] long lValue);
	};

	[
		uuid(A17BC235-A924-4FFE-8D96-22068CEA9959),
		helpstring("EventFiringObject Class")
	]
	coclass EventFiringObject
	{
		[default] interface IEventFiringObject;
		[default, source] dispinterface _IEventFiringObjectEvents;
	};
};