Gas & Electric Dryer?

Now excuse me if this sounds really stupid, I’ve owned the same W/D pair my wife and I purchased in 99. Yesterday I went and picked up a W/D pair my brother had in storage for my Mom. After I got there yesterday I realized they had no gas hook up and it was set for electricity. Fine, says I, we’ll just pick up an electric today and sell the gas one. My Mom then says, ‘too bad it’s not like my old one, you can switch it from gas to electric’.

Now this morning my sister called and has told me a story about also having a dryer that could be switched from gas to electric. I’ve never heard of such a thing, I’ve always assumed that dryers were either gas or electric not both. So what’s the scoop?