mouseover, mouseout專用: relatedTarget, fromElement, toElement

Refers to an Element that is related to the target node of the event. For mouseover events, it is the Element the mouse left when it moved over the target. For mouseout events, it is the Element the mouse entered when leaving the target. relatedTarget is undefined for other types of mouse events.

fromElement, toElement

fromElement specifies the document element that the mouse came from for mouseover events. toElement specifies the document element that the mouse has moved to for mouseout events. Comparable to the relatedTarget property of the DOM MouseEvent object.