Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Writer/Xlsx/Rels.php
public function writeHeaderFooterDrawingRelationships(\PhpOffice\PhpSpreadsheet\Worksheet\Worksheet $pWorksheet)
    {
        // Create XML writer
        $objWriter = null;
        if ($this->getParentWriter()->getUseDiskCaching()) {
            $objWriter = new XMLWriter(XMLWriter::STORAGE_DISK, $this->getParentWriter()->getDiskCachingDirectory());
        } else {
            $objWriter = new XMLWriter(XMLWriter::STORAGE_MEMORY);
        }

        // XML header
        $objWriter->startDocument('1.0', 'UTF-8', 'yes');

        // Relationships
        $objWriter->startElement('Relationships');
        $objWriter->writeAttribute('xmlns', 'http://schemas.openxmlformats.org/package/2006/relationships');

        // Loop through images and write relationships
        foreach ($pWorksheet->getHeaderFooter()->getImages() as $key => $value) {
            // Write relationship for image drawing
            $this->writeRelationship(
                $objWriter,
                $key,
                'http://schemas.openxmlformats.org/officeDocument/2006/relationships/image',
                '../media/' . $value->getIndexedFilename()
            );
        }

        $objWriter->endElement();

        return $objWriter->getData();
    }
public function writeHeaderFooterDrawingRelationships(\PhpOffice\PhpSpreadsheet\Worksheet\Worksheet $pWorksheet)
    {
        // Create XML writer
        $objWriter = null;
        if ($this->getParentWriter()->getUseDiskCaching()) {
            $objWriter = new XMLWriter(XMLWriter::STORAGE_DISK, $this->getParentWriter()->getDiskCachingDirectory());
        } else {
            $objWriter = new XMLWriter(XMLWriter::STORAGE_MEMORY);
        }

        // XML header
        $objWriter->startDocument('1.0', 'UTF-8', 'yes');

        // Relationships
        $objWriter->startElement('Relationships');
        $objWriter->writeAttribute('xmlns', 'http://schemas.openxmlformats.org/package/2006/relationships');

        // Loop through images and write relationships
        foreach ($pWorksheet->getHeaderFooter()->getImages() as $key => $value) {
            // Write relationship for image drawing
            $this->writeRelationship(
                $objWriter,
                $key,
                'http://schemas.openxmlformats.org/officeDocument/2006/relationships/image',
                '../media/' . $value->getIndexedFilename()
            );
        }

        $objWriter->endElement();

        return $objWriter->getData();
    }
Write header/footer drawing relationships to XML format.

@param \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet $pWorksheet

@throws WriterException

@return string XML Output