This allows alternate ways to enable debugging. NONE means no alternate methods are allowed. URL means when the keyword SMARTY_DEBUG is found in the QUERY_STRING, debugging is enabled for that invocation of the script. If $debugging is TRUE, this value is ignored.

<?php
// shows debug console only on localhost ie
// http://localhost/script.php?foo=bar&SMARTY_DEBUG
$smarty->debugging = false; // the default
$smarty->debugging_ctrl = ($_SERVER['SERVER_NAME'] == 'localhost') ? 'URL' : 'NONE';
?>

See also debugging console section and $debugging.