@uastronomer @revk Exactly, the reversal is through the plane of the mirror - it's just how we conventionally rotate to look at the image which is confusing.

If I'm looking north at a mirror in front of me, so to the north, then the image of my head is still up, of my feet is still down, of my right hand is still to the east and of my left hand still to the west.

However the image of my front is to the south of the image of my back, contrary to my real position.

Similarly with text. If there's some writing on a wall behind me in the above scenario then the round side of a letter 'P' is on the west in both the real world and in the image in the same way that the vertical bit away from the loop is still down.

Because of the north-south swap effect of the mirror, though, we're now viewing the text as if from the south - i.e., though the wall (OK, let's pretend it's text on a window).

Because of the way we tend to walk around in the world we imagine going to look at the other side of the window by walking, rotating about our vertical axis, so now we label left and right the other way round.