code: function(event, delta) {
  			var elem = (plugin.curInst && plugin.curInst.elem[0]) ||
  				$(event.target).closest('.' + plugin._getMarker())[0];
  			if (plugin.isDisabled(elem)) {
  				return;
  			}
  			var inst = plugin._getInst(elem);
  			if (inst.options.useMouseWheel) {
  				delta = (delta < 0 ? -1 : +1);
  				plugin.changeMonth(elem, -inst.options[event.ctrlKey ? 'monthsToJump' : 'monthsToStep'] * delta);
  			}
  			event.preventDefault();
  		}
docs: Increment/decrement month/year on mouse wheel activity.
  @memberof CalendarsPicker
  @private
  @param event {event} The mouse wheel event.
  @param delta {number} The amount of change.