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;
}