$re = '/^[`]\K | (?<=\G) (?>{.*?}|[^`]) \K [^{}`]+/xm';
$str = '`{string} with {exluded} words 12 nums`
`string {with} {exluded} words 12 nums`
"quoted {string} with {exluded} words and 12 nums"
"quoted string {with} exluded {words} and {12} nums"';
preg_match_all($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