$re = '/^([^,:\n\r]+):(.*(?:\R(?![^,:\n\r]+:).*)*)/m';
$str = 'Name: John Doe
Age: 23
Primary Language: English
Description: This is a multiline
description field that I want
to capture Fri, 02 Sep 2022 14:46:45 -0500
Country: Canada';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($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