Function _detectNearestEmptySortable

src/Sortable.js:230–245

(x, y)

	 * @return {HTMLElement}   Element of the first found nearest Sortable
	 */
	_detectNearestEmptySortable = function(x, y) {
		let ret;
		sortables.some((sortable) => {
			const threshold = sortable[expando].options.emptyInsertThreshold;
			if (!threshold || lastChild(sortable)) return;

			const rect = getRect(sortable),
				insideHorizontally = x >= (rect.left - threshold) && x <= (rect.right + threshold),
				insideVertically = y >= (rect.top - threshold) && y <= (rect.bottom + threshold);

			if (insideHorizontally && insideVertically) {
				return (ret = sortable);
			}
		});
		return ret;
	},

	_prepareGroup = function (options) {
		function toFn(value, pull) {