What is the significance of using $_SESSION instead of session_register() and session_is_registered() in PHP scripts?

Using $_SESSION instead of session_register() and session_is_registered() is significant because session_register() and session_is_registered() are deprecated as of PHP 5.3.0 and removed in PHP 5.4.0. Using $_SESSION is the recommended way to work with session variables in PHP scripts to ensure compatibility with newer PHP versions.

// Start the session
session_start();

// Set a session variable
$_SESSION['username'] = 'john_doe';

// Check if a session variable is set
if(isset($_SESSION['username'])) {
    echo 'Welcome back, ' . $_SESSION['username'];
}