code: function _addMergedCell(base, cellData, startRowIndex, startCellIndex) {
    const {
      colspan,
      rowspan,
      nodeName
    } = cellData;
    const colMerged = colspan > 1;
    const rowMerged = rowspan > 1;
  
    if (!colMerged && !rowMerged) {
      return;
    }
  
    const limitRowIndex = startRowIndex + rowspan;
    const limitCellIndex = startCellIndex + colspan;
  
    util.range(startRowIndex, limitRowIndex).forEach(rowIndex => {
      base[rowIndex] = base[rowIndex] || [];
  
      util.range(startCellIndex, limitCellIndex).forEach(cellIndex => {
        const mergedData = {
          nodeName
        };
  
        if (rowIndex === startRowIndex && cellIndex === startCellIndex) {
          return;
        }
  
        if (colMerged) {
          mergedData.colMergeWith = startCellIndex;
        }
  
        if (rowMerged) {
          mergedData.rowMergeWith = startRowIndex;
        }
  
        base[rowIndex][cellIndex] = mergedData;
      });
    });
  }
docs: Add merged cell.
  @param {object} base - base table data
  @param {object} cellData - cell data
  @param {number} startRowIndex - start row index
  @param {number} startCellIndex - start cell index
  @private