How to register a variable in PHP session ?

In PHP 5.3 or below, you can register a variable session_register() function. It is deprecated now and you can set directly a value in $_SESSION Global. Example:

<? php 
   // Starting session
    session_start();
   // Use of session_register() is deprecated
    $username = "PhpScots";
    session_register("username");
   // Use of $_SESSION is preferred
    $_SESSION["username"] = "PhpScots";
?>