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

        // check if we are reading drawing data
        // this is in case a free CONTINUE record occurs in other circumstances we are unaware of
        if ($this->drawingData == '') {
            // move stream pointer to next record
            $this->pos += 4 + $length;

            return;
        }

        // check if record data is at least 4 bytes long, otherwise there is no chance this is MSODRAWING data
        if ($length < 4) {
            // move stream pointer to next record
            $this->pos += 4 + $length;

            return;
        }

        // dirty check to see if CONTINUE record could be a camouflaged MSODRAWING record
        // look inside CONTINUE record to see if it looks like a part of an Escher stream
        // we know that Escher stream may be split at least at
        //        0xF003 MsofbtSpgrContainer
        //        0xF004 MsofbtSpContainer
        //        0xF00D MsofbtClientTextbox
        $validSplitPoints = [0xF003, 0xF004, 0xF00D]; // add identifiers if we find more

        $splitPoint = self::getUInt2d($recordData, 2);
        if (in_array($splitPoint, $validSplitPoints)) {
            // get spliced record data (and move pointer to next record)
            $splicedRecordData = $this->getSplicedRecordData();
            $this->drawingData .= $splicedRecordData['recordData'];

            return;
        }

        // move stream pointer to next record
        $this->pos += 4 + $length;
    }
private function readContinue()
    {
        $length = self::getUInt2d($this->data, $this->pos + 2);
        $recordData = $this->readRecordData($this->data, $this->pos + 4, $length);

        // check if we are reading drawing data
        // this is in case a free CONTINUE record occurs in other circumstances we are unaware of
        if ($this->drawingData == '') {
            // move stream pointer to next record
            $this->pos += 4 + $length;

            return;
        }

        // check if record data is at least 4 bytes long, otherwise there is no chance this is MSODRAWING data
        if ($length < 4) {
            // move stream pointer to next record
            $this->pos += 4 + $length;

            return;
        }

        // dirty check to see if CONTINUE record could be a camouflaged MSODRAWING record
        // look inside CONTINUE record to see if it looks like a part of an Escher stream
        // we know that Escher stream may be split at least at
        //        0xF003 MsofbtSpgrContainer
        //        0xF004 MsofbtSpContainer
        //        0xF00D MsofbtClientTextbox
        $validSplitPoints = [0xF003, 0xF004, 0xF00D]; // add identifiers if we find more

        $splitPoint = self::getUInt2d($recordData, 2);
        if (in_array($splitPoint, $validSplitPoints)) {
            // get spliced record data (and move pointer to next record)
            $splicedRecordData = $this->getSplicedRecordData();
            $this->drawingData .= $splicedRecordData['recordData'];

            return;
        }

        // move stream pointer to next record
        $this->pos += 4 + $length;
    }
Read a free CONTINUE record. Free CONTINUE record may be a camouflaged MSODRAWING record
When MSODRAWING data on a sheet exceeds 8224 bytes, CONTINUE records are used instead. Undocumented.
In this case, we must treat the CONTINUE record as a MSODRAWING record.