at det stilles som vilkår for indgåelse af en aftale, at medkontrahenten godkender tillægsydelser, som efter deres natur eller ifølge handelssædvane ikke har forbindelse med aftalens genstand.  
making the conclusion of contracts subject to acceptance by the other parties of supplementary obligations which, by their nature or according to commercial usage, have no connection with the subject of such contracts.  