I was going to add that most of that previous post has very little to do with folk song as I've rarely heard falsetto used except for occasional comic effect. .'
American singer Jimmy Rodgers used it all the time so did the texas drifter gobell reeves Jimmie Rodgers, was an American country, blues and folk ... Rodgers was also known as "The Singing Brakeman".
Yodelling has a lot to do with Swiss folk song