code: function (axis, row) {
                      var returnField = [];
                      if (axis !== null) {
                          if (axis._hasTimeField()) {
                              returnField.push(axis._parseDate(row[axis.timeField]));
                          } else if (axis._hasCategories()) {
                              axis.categoryFields.forEach(function (cat) {
                                  returnField.push(row[cat]);
                              }, this);
                          }
                      }
                      return returnField;
                  }
docs: The data for this series