code: @Pure
  	public double fx2docAngle(double angle) {
  		final ZoomableCanvas<?> canvas = getCanvas();
  		if (canvas.isInvertedAxisX() != canvas.isInvertedAxisY()) {
  			return -angle;
  		}
  		return angle;
  	}
docs: Transform a JavaFX angle to its document equivalent.
  
  @param angle the JavaFX angle.
  @return the document angle.