Pearse Doherty (Donegal, Sinn Fein) | Oireachtas source

The definition of "permanently incapacitated", either physically or mentally, may not refer to someone who is a child or that the person is in receipt of child benefit. It could be a next-door neighbour. Where are the definitions? They cannot be found on the Revenue website. This throws up some queries. What does "permanently mentally incapacitated" mean? There are different degrees under which that could be argued. Sometimes providing a lot of information can be confusing. I cannot find easily accessible information on this for members of the public who, for example, have an adult living at home. What does it mean when someone is "permanently mentally incapacitated"?