Using Presentation Variable in Column formula for multi select prompt

Suppose you have defined presentation variable named CountryName in country prompt.

Normally we use presentation variable as follows :

'@{CountryName}' which will show in physical query as 

'Afghanistan,Aland Islands,Albania'

By doing little research I came across below syntax

@{CountryName}['@'] which will show values as expected syntax

('Afghanistan','Aland Islands','Albania')