docs: function ChartAxis () {
      var axisLinker = function (scope, element, attrs, chartCtrl) {
          var rotate = attrs.axisRotate;
          if (rotate) {
              chartCtrl.rotateAxis();
          }
      };
  
      return {
          "require": "^c3chart",
          "restrict": "E",
          "scope": {},
          "transclude": true,
          "template": "<div ng-transclude></div>",
          "replace": true,
          "link": axisLinker
      };
  }