Remittance basis charge and self assessment return

I have a client who’s UK resident but non domiciled.  He’ll be paying the remittance basis charge for the first time this year. When completing the nominated amount section on page RR3 of the “residence, remittance basis etc” section (boxes 34 and 35) what information is typically provided in box 40? 

In the past I’ve only ever used box 40 to state that the client is non domiciled and that a remittance basis claim will result in a loss of personal allowances.

What extra information should be disclosed as a result of the nominated income/gains.  I don’t want to make it so brief as to risk the claim being denied but I don’t really want to quote chapter and verse either.

Grateful for any guidance you can give.

Thanks in advance.