https://ec.europa.eu/commission/sites/beta-political/files/customs_controls_0.pdf
https://ec.europa.eu/commission/publications/position-paper-essential-principles-citizens-rights_en
https://www.regjeringen.no/globalassets/upload/kilde/fkd/red/2004/0009/ddd/pdfv/228920-nilf_rapport_2004_9_s.pdf