@@ -, +, @@ 
   /**
     * Adds a merged region of cells (hence those cells form one).
     * If validate is true, check to make sure adding the merged region to the sheet doesn't create a corrupt workbook
     * If validate is false, skips the expensive merged region checks, but may produce a corrupt workbook.
     *
     * @param region to merge
     * @param validate whether to validate merged region
     * @return index of this region
     * @throws IllegalArgumentException if region contains fewer than 2 cells (this check is inexpensive and is performed regardless of <tt>validate</tt>)
     * @throws IllegalStateException if region intersects with a multi-cell array formula
     * @throws IllegalStateException if region intersects with an existing region on this sheet
     */
    private int addMergedRegion(CellRangeAddress region, boolean validate) {
        if (region.getNumberOfCells() < 2) {
            throw new IllegalArgumentException("Merged region " + region.formatAsString() + " must contain 2 or more cells");
        }
        region.validate(SpreadsheetVersion.EXCEL2007);
        if (validate) {
            // throw IllegalStateException if the argument CellRangeAddress intersects with
            // a multi-cell array formula defined in this sheet
            validateArrayFormulas(region);
            // Throw IllegalStateException if the argument CellRangeAddress intersects with
            // a merged region already in this sheet 
            validateMergedRegions(region);
        }
        CTMergeCells ctMergeCells = worksheet.isSetMergeCells() ? worksheet.getMergeCells() : worksheet.addNewMergeCells();
        CTMergeCell ctMergeCell = ctMergeCells.addNewMergeCell();
        ctMergeCell.setRef(region.formatAsString());
        return ctMergeCells.sizeOfMergeCellArray()-1;
    }