docs: function ChartAxisYTick() {
      var tickLinker = function (scope, element, attrs, chartCtrl) {
          var tick = {};
  
          var count = attrs.tickCount;
          if (count) {
              tick.count = count;
          }
  
          var outer = attrs.tickOuter;
          if (outer) {
              outer = angular.lowercase(outer);
              if (outer === 'true') {
                  tick.outer = true;
              }
              else if (outer === 'false') {
                  tick.outer = false;
              }
          }
  
          var tickValues = attrs.tickValues;
          if (tickValues) {
              if (tickValues.indexOf(',') > -1) {
                  tick.values = tickValues.split(',');
              } else {
                  tick.values = tickValues;
              }
          }
  
          var format = attrs.tickFormat;
          if (format) {
              tick.format = d3.format(format);
          }
  
          chartCtrl.addYTick(tick);
  
          if (attrs.tickFormatFunction) {
              chartCtrl.addYTickFormatFunction(scope.tickFormatFunction());
          }
      };
  
      return {
          "require": "^c3chart",
          "restrict": "E",
          "scope": {
              "tickFormatFunction": "&"
          },
          "replace": true,
          "link": tickLinker
      };
  }