docs: function ChartDonut() {
      var donutLinker = function (scope, element, attrs, chartCtrl) {
          var donut = {};
          if (attrs.showLabel) {
              donut.label = {"show": (attrs.showLabel === 'true')};
          }
          if (attrs.thresholdLabel) {
              if (!donut.label) {
                  donut.label = {};
              }
              donut.label.threshold = parseFloat(attrs.thresholdLabel);
          }
          if (attrs.expand) {
              donut.expand = (attrs.expand === 'true');
          }
          if (attrs.width) {
              donut.width = parseInt(attrs.width);
          }
          if (attrs.title) {
              donut.title = attrs.title;
          }
          chartCtrl.addDonut(donut);
          if (attrs.labelFormatFunction) {
              chartCtrl.addDonutLabelFormatFunction(scope.labelFormatFunction());
          }
      };
  
      return {
          require: '^c3chart',
          restrict: 'E',
          scope: {
              "labelFormatFunction": "&"
          },
          replace: true,
          link: donutLinker
      };
  }