get-event-type in scroll-event%

Returns the type of the event, one of the following:

• 'top -- user clicked a scroll-to-top button

• 'bottom -- user clicked a scroll-to-bottom button

• 'line-up -- user clicked an arrow to scroll up or left one step

• 'line-down -- user clicked an arrow to scroll down or right one step

• 'page-up -- user clicked an arrow to scroll up or left one page

• 'page-down -- user clicked an arrow to scroll down or right one page

• 'thumb -- user dragged the scroll position indicator

• (send a-scroll-event get-event-type) -> symbol in '(top bottom line-up line-down page-up page-down thumb)