Best way to document AJAX + PHP code?

function OutputJs($Content) {
    ob_start();
    echo $Content;
    $expires = DAY_IN_S;
    header("Content-type: x-javascript");
    header('Content-Length: ' . ob_get_length());
    header('Cache-Control: max-age='.$expires.', must-revalidate');
    header('Pragma: public');
    header('Expires: '. gmdate('D, d M Y H:i:s', time()+$expires).'GMT');
    ob_end_flush();
}