$re = '/(?:
.?\n+ |
[[:alnum:]_](?=[^[:alnum:]_\s]) |
[^[:alnum:]_\s](?=[[:alnum:]_]) |
[^\S\n](?=[\S\n]) |
)
(
(?:
[[:alnum:]_]+ |
[^[:alnum:]_\s]+ |
)
[^\S\n]*
)/xX';
$str = 'w asdf';
preg_match($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