The only issue I had was that I wasn't able to render upside-down compounds. If I put the _ before the first piece only the second piece is still right-side up. If I put the _ before both, it gives me nothing. (So I made the upside-down cardinal and chancellor the old-fashioned way.)
I guess I didn't really bother to implment that, on the assumption that rotated pieces would only be used as the conventional way to indicate fairy pieces (e.g. when typesetting diagrams) with the 6 orthodox symbols (e.g. inverted Queen = Grasshopper, inverted Knight = Nightrider...). If you have compounds, there doesn't seem to be any reason to use rotated symbols.
I guess I didn't really bother to implment that, on the assumption that rotated pieces would only be used as the conventional way to indicate fairy pieces (e.g. when typesetting diagrams) with the 6 orthodox symbols (e.g. inverted Queen = Grasshopper, inverted Knight = Nightrider...). If you have compounds, there doesn't seem to be any reason to use rotated symbols.