docs: function handleMousedown(event) {
          scope.broadcast('dragstart');
          downScrollPosition = {
              top: $el.scrollTop(),
              left: $el.scrollLeft()
          };
          downMousePosition = {
              x: event.clientX,
              y: event.clientY
          };
          $window.on('mousemove', handleMousemove);
          $window.on('mouseup', handleMouseup);
          event.preventDefault();
      }