protected function createCoreXmlFile()
    {
        $createdDate = (new \DateTime())->format(\DateTime::W3C);
        $coreXmlFileContents = <<<EOD
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:coreProperties xmlns:cp="http://schemas.openxmlformats.org/package/2006/metadata/core-properties" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:dcmitype="http://purl.org/dc/dcmitype/" xmlns:dcterms="http://purl.org/dc/terms/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <dcterms:created xsi:type="dcterms:W3CDTF">$createdDate</dcterms:created>
    <dcterms:modified xsi:type="dcterms:W3CDTF">$createdDate</dcterms:modified>
    <cp:revision>0</cp:revision>
</cp:coreProperties>
EOD;

        $this->createFileWithContents($this->docPropsFolder, self::CORE_XML_FILE_NAME, $coreXmlFileContents);

        return $this;
    }