If l is used then there needs to be the layer numbers following that.
In the tooltip syntax example, the a, h, s etc are all other options that are available for the on keyin.
so what's the command to turn on or off all layers?
The Help menu suggests "of l a"
I tried some other combinations and I had no success.
It turns out that this is a defect or the Help menu is incorrect.
Customer Support made it as a Defect Report / Enhancement Request # 01100059