A mandate before witnesses:

3.5 What should I include in a mandate in case of incapacity?
[Student Manual, page 18]

You can include whatever you like in a mandate. You can:

3.6 Should I tell anyone about my mandate in case of incapacity?
[Student Manual, page 19]

It is a good idea to tell someone you have a mandate, but you do not have to tell them what is in it. It is your decision. You should tell the person you have named as mandatary about the mandate, because he/she has to agree to accept this responsibility. You can tell your mandatary where to find the original copy.