I am new with advance php. Please can you explain what this function does?

```
ini_set('session.use_trans_sid', 0);

```

I have particular file named index.php in which if I start session I get following error on this function.

> 
> Warning: ini\_set() [function.ini-set]: A session is active. You cannot change the session module's ini settings at this time in [...]/main.inc.php on line 35
> 
> 
> 

I have installed a module and that module is removing all main page sessions, which is why I put a condition on it - to check `session_start()` and that particular condition for session.