// throw IllegalStateException if the argument CellRangeAddress intersects with
// a multi-cell array formula defined in this sheet
validateArrayFormulas(region);
CTMergeCells ctMergeCells = worksheet.isSetMergeCells() ? worksheet.getMergeCells() : worksheet.addNewMergeCells();
CTMergeCell ctMergeCell = ctMergeCells.addNewMergeCell();
ctMergeCell.setRef(region.formatAsString());
return ctMergeCells.sizeOfMergeCellArray();
}