How can including a PHP file affect the session variables and session ID in a script, and what precautions should be taken?

Including a PHP file can potentially affect the session variables and session ID in a script if the included file modifies or accesses the session data. To prevent any conflicts or unexpected behavior, it is important to handle session_start() and session_write_close() properly in both the main script and the included file.

// main_script.php
session_start();
// include the file
include 'included_file.php';
session_write_close();

// included_file.php
session_start();
// code that accesses or modifies session variables
session_write_close();