[cssom-view-1] Type of event to append to pending scroll events when an element gets scrolled?

[tidoust]

In Scrolling, the algorithm for "Whenever an element gets scrolled (whether in response to user interaction or by an API)" has:

3. If the element is already in doc’s pending scroll events, abort these steps.
4. Append the element to doc’s pending scroll events.

But the pending scroll events list stores pairs of (EventTarget, DOMString), not only an event target. What type of event should be added to the list along with the element?