Single Comment

Well, the main text says:

The latter is specified by the directional modifiers on the continuation leg, and is triggered by a diagonal direction specification causing a 45-degree change in direction (as directions are always relative to the previous leg).

So there is nothing new in the use of fs here; it has always meant 'diagonally forward', i.e. at an angle of 45-degrees to 'forward'. It is just that 'forward' is a relative notion. And frankly, I don't see how that could be different. The moves of a chess piece start off in many different directions, so if you want to describe a move with a fixed shape, it is only the angle between the steps that count. An absolute orientation would be useless; it would be different for each move of the symmetry-equivalent set. Angles must always be given compared to some frame of reference; for the first step the piece is still in the origin, and the symmetry is not yet broken, so we take the player as the reference.

[Edit] As the old text apparently was not clear enough, I moved part of what was hidden in the more-about-a box to the XBetza section, and also added some more explanation there. I completely rewrote the content of the hidden box, to make more like a reference guide than an explanation.