code: function (scrollOffset) {
              var alignAttr = this.group.alignAttr,
                translateY,
                clipHeight = this.clipHeight || this.legendHeight;
  
              if (alignAttr) {
                  translateY = alignAttr.translateY;
                  each(this.allItems, function (item) {
                      var checkbox = item.checkbox,
                        top;
  
                      if (checkbox) {
                          top = (translateY + checkbox.y + (scrollOffset || 0) + 3);
                          css(checkbox, {
                              left: (alignAttr.translateX + item.checkboxOffset + checkbox.x - 20) + PX,
                              top: top + PX,
                              display: top > translateY - 6 && top < translateY + clipHeight - 6 ? '' : NONE
                          });
                      }
                  });
              }
          }
docs: Position the checkboxes after the width is determined