Borders, Citizenship and Immigration Bill [HL]

I apologise for a short exercise in parsing, but the Minister may be able to help me by confirming that I understood this correctly. General customs functions are alluded to in the first four lines, from Part 1 downwards, and a definition is given in Clause 1(8): "““In this Part ‘general customs function’ means a function exercisable in relation to a general customs matter””." That does not, of itself, tell us what a general customs matter is. I realise that subsection 2(a) to (e) allude to a general customs matter. Am I right in thinking that, patently, revenue customs functions fall within subsection 2 (a) to (e) but that some of the latter are matters that are clearly the responsibility of the commissioners but not actually cash revenue issues? It would be helpful if the Minister gave us a phrase that described those functions that remain with HMRC but which are not specifically tax revenue. I hope that question is clear. If it is not, I would be glad to clarify it.