Correct me if I'm wrong but as far as I can see this excerpt from htmlsite.CloseDocument() cannot possibly be correct code.

container.Resize -= new EventHandler(this.Container_Resize);

The -= operator removes a delegate instance from the collection of delegates implied by an event declaration. The code above manufactures a NEW instance and it therefore won't be found, and therefore won't be removed. This code, though legal, has no effect other than slightly increasing transient memory consumption.

If you want to unhitch from the event you need to keep a reference to the delegate instance and pass that. So htmlsite needs a member

EventHandler containerResizeDelegateInstance;

which must be initialized in the constructor

containerResizeDelegateInstance = new EventHandler(Container_Resize);

You (un)bind it like this

container.Resize += containerResizeDelegateInstance;
container.Resize -= containerResizeDelegateInstance;

Your 2nd approach should work fine too; but although the code looks odd it is the documented way to remove an event handler if you haven't kept a reference to the delegate (which is the norm). I suppose the logic is that the "new" delegate references the same method.

Tim