$_SERVER['HTTP_REFERER'] Generally, you don't need using function isset() to test the existence of every $_SERVER element before using, because they seems always available to use.… Read More »Notice: Undefined index: HTTP_REFER
$_SERVER['QUERY_STRING'] Let's see a snippet of PHP code, which will generate three similar output: <?php echo $_SERVER['QUERY_STRING'] . "<br />"; echo urldecode($_SERVER['QUERY_STRING']) . "<br />";… Read More »How to Use $_SERVER['QUERY_STRING'] Properly