Please help document headers_sent()

Hello- headers_sent() has two new parameters as of PHP 4.3.0, these are passed in by reference. I see no need to have to do: $file = 'file.php'; $line = 4; headers_sent($file, $line); When one could simply do this: headers_sent('file.php', 4); But we can't, we get this error: Fatal error: Only variables can be passed by reference This doesn't seem important, forcing one to use variables here seems odd, why? Yes & is in the proto but afaict it shouldn't be. On a related note, I tried and failed to return anything other then 1 while using these optional parameters. I can't even tell if it's reading the file. If someone could explain a little more that would be very cool. Regards, Philip