How to use an underbraider on a vintage sewing machine - 1916 Singer 99K

The underbraider is a very useful attachment. It guides narrow braid or ribbon underneath the work so that it is sewn on with the bobbin thread. It is ideal for making edged hems on clothing, and looks particularly pretty on little girls' dresses. The braid must be narrow enough to pass freely though the guide on the underbraider.
The machine used in this video is a 1916 Singer 99K.