Php $_SERVER some key value

<?php

$_SERVER["QUERY_STRING"] // index.php?x=1&y=2
$_SERVER["REMOTE_ADDR"]  // client  ip
$_SERVER["HTTP_REFERER"] // http://domain.com/blog/category/11
$_SERVER["REQUEST_URI"]  // /blog/category/11
$_SERVER["SCRIPT_NAME"]  // index.php
$_SERVER["SERVER_NAME"]  // domain.com
$_SERVER["HTTP_HOST"]  // domain.com
$_SERVER["DOCUMENT_ROOT"]  //  /home/username/public_html

?>