EBU Single Rulebook Q&A 11 February 2014 2014_837 Large exposures - major trading currencies in overnight transactions

How are the major trading currencies to be determined under Article 400(2)(f) of the CRR? Clarification is needed on what is to be considered a major trading currency under Article 400(2)(f). In Article 400(2)(f) it's written that institutions may exempt all the exposures if these are overnight transactions and are not denominated in a major trading currency.