在IHTMLElement事件处理程序中没有获取事件参数

I've added a callback to an IHTMLElement instance but when the IDispatch::Invoke is called for the event, there are never any arguments (i.e. the pDispParams->cArgs and pDispParams->cNamedArgs are always 0). For example, I add a callback for an onmouseup event. From what I can tell, a callback for this event is supposed to receive a MouseEvent object. Is that correct? If so, what do I need to do to ensure this happens? I've added a callback to an IHTMLElement instan