source: inc/alerts-err.php

<?php
/**
 * If the "err" parameter is in the page URL, display the corresponding error message.
 */
?>
<?php if ((isset($_GET['err'])) && (! empty($_GET['err']))) { ?>
        <div class="alert alert-danger" role="alert">
                <strong>ERROR:</strong>
                <?php
                switch ($_GET['err']) {
                        case 'no_id':
                                echo 'Missing parameter.'; break;
                        case 'bad_id':
                                echo 'Item not found.'; break;
                        case 'missing_params':
                                echo 'Some parameters are missing.'; break;
                        case 'wrong_params':
                                echo 'Some parameters are incorrect.'; break;
                        case 'permission_error':
                                echo 'You do not have enough permissions.'; break;
                        default:
                                echo 'An unknown error has occurred.';
                }
                ?>
        </div>
<?php } ?>