character string or a vector of strings. Supported values are accounting sign, afghani,
armenian dram, austral, baht, bitcoin, boliviano, cent, cedi, currency, dollar,
dong, drachma, dutch guilder, euro, franc, georgian lari, german penny, hryvnia,
indian rupee, iranian rial, kip, lari, lira, livre tournois, manat, mark, new shekel,
pakistani rupee, peso, pound, quetzal, real, rial, ruble, shekel, spesmilo, syrian pound,
tenge, tugrik, turkish lira, won, yen, yuan.