问题 说起$_REQUEST，大家都知道的是它是$_GET和$_POST的集合。但是如果你有心的话，查一下文档，会看到：
$_REQUEST
An associative array that by default contains the contents of $_GET, $_POST and $_COOKIE.
这里说$_REQUEST默认是$_GET, $_POST, $_COOKIE的集合，结果我使用我本地的php查看了一下发现只有$_GET, $_POST, 没有$_COOKIE！！ 难道文档是错的？
答案 其实changelog中有给出解释：
版本5.3以上，php.ini中有request_order属性来设置$_REQUEST。查了下php.ini， request_order设置成为了GP（Get and Post）。
request_order的官网描述：
request_order string
This directive describes the order in which PHP registers GET, POST and Cookie variables into the _REQUEST array. Registration is done from left to right, newer values override older values.
If this directive is not set, variables_order is used for $_REQUEST contents.
Note that the default distribution php.ini files does not contain the 'C' for cookies, due to security concerns.
