<?php
/*
* libs/functions.php
*/
    xssClean($input) {
        return htmlspecialchars($input); //this way, you can reuse and improve your script from time to time
    }
?>

<?php
    require_once 'db/db.php';
    require_once 'libs/functions.php';
    $output = 'Hello World'
    echo xssClean($output);
?>