cancel event fires when the user indicates a wish to dismiss a
<dialog>. This event handler prevents the event from bubbling, so any
parent handlers are not notified of the event.
target.oncancel = functionRef;
oncancel handler can be assigned to an object at a time. You may
prefer to use the
EventTarget.addEventListener() method instead, since
it's more flexible.
|HTML Living Standard
The definition of 'oncancel' in that specification.
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