In Today's AWAD it says:
"In such writing, each letter on the alternate lines was written as in a mirror image or rotated 180 degrees."
A 'mirror-image' and 'rotated 180 degrees' are two very different things. The definition immediately made me think of a third option: the letters are NOT mirrorred but written in reverse order.
So, which is it?

BTW: I mow my lawn by making parallel strokes in the same direction. In this way the discharge throws grass into my [next] path so it can be further cut rather than left to lie on the cut grass in clumps.

"I am certain there is too much certainty in the world" -Michael Crichton