function defaultFormatter() {
			var pThis = this,
				items = pThis.points || splat(pThis),
				series = items[0].series,
				s;

			// build the header
			s = [series.tooltipHeaderFormatter(items[0].key)];

			// build the values
			each(items, function (item) {
				series = item.series;
				s.push((series.tooltipFormatter && series.tooltipFormatter(item)) ||
					item.point.tooltipFormatter(series.tooltipOptions.pointFormat));
			});
			
			// footer
			s.push(options.footerFormat || '');
			
			return s.join('');
		}
In case no user defined formatter is given, this will be used