function eventAtRatio(event, $item, ratios) {
            $item.trigger($.Event(event, {
                clientX: $item.offset().left + (ratios[0] * $item.width()),
                clientY: $item.offset().top + (ratios[1] * $item.height())
            }));
        }
Simulate the given event with clientX/clientY specified by the given
ratios of the item's actual width/height (offset by the left/top of the
item).
@param {string} event The name of the event to simulate.
@param {object} $item A jQuery object to trigger the event on.
@param {Array.<number>} ratios Numbers between 0 and 1 indicating the x and y positions of the
     event relative to the item's width and height.