docs: function Selection () {
      var selectionLinker = function (scope, element, attrs, chartCtrl) {
          var enabled = attrs.enabled;
          var grouped = attrs.grouped;
          var multiple = attrs.multiple;
  
          if (enabled && enabled === 'true') {
              var selection = {"enabled": true};
              if (grouped && grouped === 'true') {
                  selection.grouped = true;
              }
              if (multiple && multiple === 'true') {
                  selection.multiple = true;
              }
              chartCtrl.addSelection(selection);
          }
      };
  
      return {
          "require": "^c3chart",
          "restrict": "E",
          "scope": {},
          "replace": true,
          "link": selectionLinker
      };
  }