docs: function generateDecoration(radicand) {
                  var shape = new kity.Path(), // 命名为a以便于精简表达式
                  a = SHAPE_DATA_WIDTH, h = radicand.getHeight() / 3, drawer = shape.getDrawer();
                  // 根号尾部左上角开始
                  drawer.moveTo(0, cos15 * a * 6);
                  drawer.lineBy(sin15 * a, cos15 * a);
                  drawer.lineBy(cos15 * a * 3, -sin15 * a * 3);
                  drawer.lineBy(tan15 * h, h);
                  drawer.lineBy(sin15 * a * 3, -cos15 * a * 3);
                  drawer.lineBy(-sin15 * h, -h);
                  drawer.close();
                  return shape.fill("black");
              }