Don't forget, because $_REQUEST is a different variable than $_GET and $_POST, it is treated as such in PHP -- modifying $_GET or $_POST elements at runtime will not affect the ellements in $_REQUEST, nor vice versa.

e.g:

<?php

$_GET['foo'] = 'a';
$_POST['bar'] = 'b';
var_dump($_GET); // Element 'foo' is string(1) "a"
var_dump($_POST); // Element 'bar' is string(1) "b"
var_dump($_REQUEST); // Does not contain elements 'foo' or 'bar'

?>

If you want to evaluate $_GET and $_POST variables by a single token without including $_COOKIE in the mix, use  $_SERVER['REQUEST_METHOD'] to identify the method used and set up a switch block accordingly, e.g:

<?php

switch($_SERVER['REQUEST_METHOD'])
{
case 'GET': $the_request = &$_GET; break;
case 'POST': $the_request = &$_POST; break;
.
. // Etc.
.
default:
}
?>

In PHP version 7.0 with the default settings.+, $_REQUEST array does not contain cookies.

The default php.ini on your system as of in PHP 5.3.0 may exclude cookies from $_REQUEST.  The request_order ini directive specifies what goes in the $_REQUEST array; if that does not exist, then the variables_order directive does.  Your distribution's php.ini may exclude cookies by default, so beware.

To access $_POST, $_GET, etc, use the function filter_input(TYPE, varname, filter) to ensure that your data is clean. 

Also, I was brought up to believe that modifying superglobals is a BAD idea. I stand by this belief and would recommend you do too