Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Reader/Xls.php
private function readMulRk()
    {
        $length = self::getUInt2d($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
        $colFirst = self::getUInt2d($recordData, 2);

        // offset: var; size: 2; index to last column
        $colLast = self::getUInt2d($recordData, $length - 2);
        $columns = $colLast - $colFirst + 1;

        // offset within record data
        $offset = 4;

        for ($i = 1; $i <= $columns; ++$i) {
            $columnString = Coordinate::stringFromColumnIndex($colFirst + $i);

            // Read cell?
            if (($this->getReadFilter() !== null) && $this->getReadFilter()->readCell($columnString, $row + 1, $this->phpSheet->getTitle())) {
                // offset: var; size: 2; index to XF record
                $xfIndex = self::getUInt2d($recordData, $offset);

                // offset: var; size: 4; RK value
                $numValue = self::getIEEE754(self::getInt4d($recordData, $offset + 2));
                $cell = $this->phpSheet->getCell($columnString . ($row + 1));
                if (!$this->readDataOnly) {
                    // add style
                    $cell->setXfIndex($this->mapCellXfIndex[$xfIndex]);
                }

                // add cell value
                $cell->setValueExplicit($numValue, DataType::TYPE_NUMERIC);
            }

            $offset += 6;
        }
    }
private function readMulRk()
    {
        $length = self::getUInt2d($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
        $colFirst = self::getUInt2d($recordData, 2);

        // offset: var; size: 2; index to last column
        $colLast = self::getUInt2d($recordData, $length - 2);
        $columns = $colLast - $colFirst + 1;

        // offset within record data
        $offset = 4;

        for ($i = 1; $i <= $columns; ++$i) {
            $columnString = Coordinate::stringFromColumnIndex($colFirst + $i);

            // Read cell?
            if (($this->getReadFilter() !== null) && $this->getReadFilter()->readCell($columnString, $row + 1, $this->phpSheet->getTitle())) {
                // offset: var; size: 2; index to XF record
                $xfIndex = self::getUInt2d($recordData, $offset);

                // offset: var; size: 4; RK value
                $numValue = self::getIEEE754(self::getInt4d($recordData, $offset + 2));
                $cell = $this->phpSheet->getCell($columnString . ($row + 1));
                if (!$this->readDataOnly) {
                    // add style
                    $cell->setXfIndex($this->mapCellXfIndex[$xfIndex]);
                }

                // add cell value
                $cell->setValueExplicit($numValue, DataType::TYPE_NUMERIC);
            }

            $offset += 6;
        }
    }
Read MULRK record
This record represents a cell range containing RK value
cells. All cells are located in the same row.

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