Here's a list of the reserved $_SERVER[] array that you may need later 🙂
$_SERVER['SERVER_NAME'];
$_SERVER['DOCUMENT_ROOT'];
$_SERVER['PHP_SELF'];
$_SERVER['argv'];
$_SERVER['argc'];
$_SERVER['GATEWAY_INTERFACE'];
$_SERVER['SERVER_SOFTWARE'];
$_SERVER['SERVER_PROTOCOL'];
$_SERVER['REQUEST_METHOD'];
$_SERVER['REQUEST_TIME'];
$_SERVER['QUERY_STRING'];
$_SERVER['HTTP_ACCEPT'];
$_SERVER['HTTP_ACCEPT_CHARSET'];
$_SERVER['HTTP_ACCEPT_ENCODING'];
$_SERVER['HTTP_ACCEPT_LANGUAGE'];
$_SERVER['HTTP_CONNECTION'];
$_SERVER['HTTP_HOST'];
$_SERVER['HTTP_REFERER'];
$_SERVER['HTTP_USER_AGENT'];
$_SERVER['REMOTE_ADDR'];
$_SERVER['REMOTE_HOST'];
$_SERVER['REMOTE_PORT'];
$_SERVER['SCRIPT_FILENAME'];
$_SERVER['SERVER_ADMIN'];
$_SERVER['SERVER_PORT'];
$_SERVER['SERVER_SIGNATURE'];
$_SERVER['PATH_TRANSLATED'];
$_SERVER['SCRIPT_NAME'];
$_SERVER['REQUEST_URI'];
$_SERVER['PHP_AUTH_USER'];
$_SERVER['PHP_AUTH_PW'];
$_SERVER['AUTH_TYPE'];