$re = '/<!\[CDATA\[(.*|\n|.*\n.*)&#x.....;(.*|\n|.*\n.*)]]/';
$str = '
<journal-meta>
<issn>Modern data <![CDATA[ data is <>?":{}|\\][;\'.
/, ']]> is needed with dummy content. we are good to go.</issn>
<issn>Modern data <![CDATA[ data is not proper ' sdgfs ]]> is needed with dummy content. we are good to go.</issn>
<issn>Modern data <![CDATA[
data is not proper ']]> is needed with dummy content. ' we are good to go.</issn>
<issn>Modern data <![CDATA[
']]> is needed with dummy content. we are good to go.</issn>
<issn2><![CDATA[é]]>Modern data is needed with dummy content. we are good to go.</issn2>
<issn3><![CDATA[']]>Modern data is needed with dummy content. we are good to go.</issn3>
<issn4><![CDATA[&]]>Modern data is needed with dummy content. we are good to go.</issn4>
<issn5><![CDATA[–]]>Modern data is needed with dummy content. we are good to go.</issn5>
</journal-meta>';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php