Laying a yankee bet.

Hello people,
                       Right I'm not to sure about this but I was reading somewhere about laying a yankee on betfair. I've been on betfair a while and never thought about it until I found this article. I don't have a clue wether you could or never have been able to or still can, I was just wondering if anyone new how to do it because I picked out my 4 horses and there was no option to lay. Any help would be much appreciated.

The Sheepshagger, Welshie5121.