$re = '/[a-zA-Z]+(?=\s+in\s+\[\s*[a-zA-Z-]+(?:\s*,\s*[a-zA-Z-]+)*\s*])|(?:\G(?!^)\s*,\s*|(?<=[a-zA-Z])\s+in\s+\[\s*)\K[a-zA-Z-]+(?=(?:\s*,\s*[a-zA-Z-]+)*\s*])/m';
$str = 'location in [chambre, cuisine, salle-de-bain, jardin]';
preg_match_all($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