Ahhh... but the trade name for that type of hinge is a piano hinge, it is cut to length as required and the hinge pin anchored by either a centre punch indentation the through the fixed section to the pin or a tack of weld to stop it dropping out, this way the pin remains an active part of the assembly creating a better cycle life and easier operation. The hinges on a bus bi fold door are still referred to as piano hinges.
Maybe it should have read "it has a piano hinged lid
As for the "course" file, maybe it's a training session on how to use one properly

But seriosly, they are only designed the cut in one direction, forward, dragging them backwards while presure is applied damages the cutting teeth by curling them over so the shape face is no longer available for the next forward stroke.