Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Reader/Xls.php
private function readMulBlank()
    {
        $length = self::getUInt2d($this->data, $this->pos + 2);
        $recordData = $this->readRecordData($this->data, $this->pos + 4, $length);

        // move stream pointer to next record
        $this->pos += 4 + $length;

        // offset: 0; size: 2; index to row
        $row = self::getUInt2d($recordData, 0);

        // offset: 2; size: 2; index to first column
        $fc = self::getUInt2d($recordData, 2);

        // offset: 4; size: 2 x nc; list of indexes to XF records
        // add style information
        if (!$this->readDataOnly && $this->readEmptyCells) {
            for ($i = 0; $i < $length / 2 - 3; ++$i) {
                $columnString = Coordinate::stringFromColumnIndex($fc + $i + 1);

                // Read cell?
                if (($this->getReadFilter() !== null) && $this->getReadFilter()->readCell($columnString, $row + 1, $this->phpSheet->getTitle())) {
                    $xfIndex = self::getUInt2d($recordData, 4 + 2 * $i);
                    $this->phpSheet->getCell($columnString . ($row + 1))->setXfIndex($this->mapCellXfIndex[$xfIndex]);
                }
            }
        }

        // offset: 6; size 2; index to last column (not needed)
    }
private function readMulBlank()
    {
        $length = self::getUInt2d($this->data, $this->pos + 2);
        $recordData = $this->readRecordData($this->data, $this->pos + 4, $length);

        // move stream pointer to next record
        $this->pos += 4 + $length;

        // offset: 0; size: 2; index to row
        $row = self::getUInt2d($recordData, 0);

        // offset: 2; size: 2; index to first column
        $fc = self::getUInt2d($recordData, 2);

        // offset: 4; size: 2 x nc; list of indexes to XF records
        // add style information
        if (!$this->readDataOnly && $this->readEmptyCells) {
            for ($i = 0; $i < $length / 2 - 3; ++$i) {
                $columnString = Coordinate::stringFromColumnIndex($fc + $i + 1);

                // Read cell?
                if (($this->getReadFilter() !== null) && $this->getReadFilter()->readCell($columnString, $row + 1, $this->phpSheet->getTitle())) {
                    $xfIndex = self::getUInt2d($recordData, 4 + 2 * $i);
                    $this->phpSheet->getCell($columnString . ($row + 1))->setXfIndex($this->mapCellXfIndex[$xfIndex]);
                }
            }
        }

        // offset: 6; size 2; index to last column (not needed)
    }
Read MULBLANK record
This record represents a cell range of empty cells. All
cells are located in the same row.

--    "OpenOffice.org's Documentation of the Microsoft
Excel File Format"