code: function (cell) {
              var cellInfo = this.getCellInfo(cell),
                  downRowIndex = cellInfo.rowIndex + cellInfo.rowSpan,
                  downCellInfo = this.indexTable[downRowIndex][cellInfo.colIndex],
                  downCell = this.getCell(downCellInfo.rowIndex, downCellInfo.cellIndex);
              cell.rowSpan = cellInfo.rowSpan + downCellInfo.rowSpan;
              cell.removeAttribute("height");
              this.moveContent(cell, downCell);
              this.deleteCell(downCell, downCellInfo.rowIndex);
              this.update();
          }
docs: 向下合并单元格