These are lists used within the document to provide you with what the possible options are within a given field.
Countries
Based on the ISO Code List
https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2
There are also some special codes through HMRC for Isle of Man, Jersey, Guernsey
Also see https://www.uktradeinfo.com/CodesAndGuides/Pages/CodesGuides.aspx
Currencies
Based on ISO 4217 - https://en.wikipedia.org/wiki/ISO_4217
Also See https://www.uktradeinfo.com/CodesAndGuides/Pages/CodesGuides.aspx
Trade Terms
The trade terms are codes issued by HMRC which are used to define INCOTerms
IncoTerms are explained on this wiki https://en.wikipedia.org/wiki/Incoterms
Also see https://www.uktradeinfo.com/CodesAndGuides/Pages/CodesGuides.asp