code: public void setCellMerge(final int rowIndex, final int colIndex, final int rowMerge,
                               final int columnMerge) throws IOException {
          this.builder.setCellMerge(this, this.appender, rowIndex, colIndex, rowMerge, columnMerge);
      }
docs: Set a span over cells
  
  @param rowIndex    the top row
  @param colIndex    the leftmost col
  @param rowMerge    the number of rows
  @param columnMerge the number of cols
  @throws IOException if an error occurs