Description:
------------
It would be nice if preg_replace_callback had a "userdata" parameter.

Example:
$string = "[thing 1] foo [thing 2]";
$things = array( 1 => "One thing", 2 => "Other thing");

function replace_callback($match, $data) {
    return $data[$match[1]];
}

echo preg_replace_callback('/\[thing (\d+)\]/', 'replace_callback', $string, -1, $data);

Would Output:
One thing foo Other thing