This example shows how to use callback functions `onAdd`, `onMove`, `onMoving`, `onUpdate`, and `onRemove`. The `onMoving` function updates an item while dragging, and can be used to prevent the item from being drawn at disallowed or infeasible timeslots. In this example, the items cannot be moved outside of the month April 2013. The other callback functions are called after an add, move, update, or remove action has taken place, and can be used to cancel these actions.