Hi experts. I would like to know how to allow http refer from more than 1 site.

For example

<?php
$domain='example.net';
$referrer = $_SERVER['HTTP_REFERER'];
if (@preg_match("/example.net/",$referrer)) {
} else {
header('Location: http://www.example.net/404.php');
};
?>

This code works if I open links from example.net, but I want to allow example1.net and example2.net as well to access the links.

How do I do this? If anyone could help me with this, it would highly be appreciated.