$re = '/\[(?P<tag>[A-Za-z0-9]+)\](?P<text>[А-Яа-яA-Za-z0-9- ,\.\(\)]+)(?=\[)/m';
$str = '[m1]Эрэн-Хото [i](городской уезд автономного района)[/i][/m1]';
preg_match_all($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