code: function drawDonutHole(layer) {
  			if (options.series.pie.innerRadius > 0) {
  
  				// subtract the center
  
  				layer.save();
  				var innerRadius = options.series.pie.innerRadius > 1 ? options.series.pie.innerRadius : maxRadius * options.series.pie.innerRadius;
  				layer.globalCompositeOperation = "destination-out"; // this does not work with excanvas, but it will fall back to using the stroke color
  				layer.beginPath();
  				layer.fillStyle = options.series.pie.stroke.color;
  				layer.arc(0, 0, innerRadius, 0, Math.PI * 2, false);
  				layer.fill();
  				layer.closePath();
  				layer.restore();
  
  				// add inner stroke
  
  				layer.save();
  				layer.beginPath();
  				layer.strokeStyle = options.series.pie.stroke.color;
  				layer.arc(0, 0, innerRadius, 0, Math.PI * 2, false);
  				layer.stroke();
  				layer.closePath();
  				layer.restore();
  
  				// TODO: add extra shadow inside hole (with a mask) if the pie is tilted.
  			}
  		}
docs: end draw function Placed here because it needs to be accessed from multiple locations