docs: function ChartPie () {
      var pieLinker = function (scope, element, attrs, chartCtrl) {
          var pie = {};
          if (attrs.showLabel) {
              pie.label = {"show": (attrs.showLabel === 'true')};
          }
          if (attrs.thresholdLabel) {
              if (!pie.label) {
                  pie.label = {};
              }
              pie.label.threshold = parseFloat(attrs.thresholdLabel);
          }
          if (attrs.expand) {
              pie.expand = (attrs.expand === 'true');
          }
          chartCtrl.addPie(pie);
          if (attrs.labelFormatFunction) {
              chartCtrl.addPieLabelFormatFunction(scope.labelFormatFunction());
          }
      };
  
      return {
          require: '^c3chart',
          restrict: 'E',
          scope: {
              "labelFormatFunction": "&"
          },
          replace: true,
          link: pieLinker
      };
  }