Treaty on the Functioning of the EU

Some of us are trying to work out whether there might be an element more of figment than fig leaf about what we have just heard. Can the Secretary of State help us to understand the difference between the opt-out measures and the opt-in measures by explaining whether, when Northern Ireland citizens find themselves detained by Spanish police at an airport, only to be confronted by MI5 officers making nefarious propositions with menaces, those actions are covered under opt-in measures or under proposed opt-out measures?