When is the use of the vehicle horn appropriate and legal under the Highway Code?

1. To express frustration at a driver who is slow to move at a green light
2. To warn other road users of your presence or impending danger where vision is obscured
3. To greet friends or acquaintances walking on the sidewalk
4. At all times while driving in residential zones between 11:00 p.m. and 6:00 a.m.