1. It is not, it is a scheme offered by a company in the event of restructuring or downsizing
2. It is up to the company to decide what type of workers or section or department to be offered. However, the company should be very careful in formulating such a scheme and expert advice should be sought.
3. Staff can always reject in the scheme is not attractive.
4. I don't know if there is a formula but come company may use the Employment(Termination and Layoff Benefits) Regulations as a general guide.