$1                         $2
|----|          |--------------------------------|
<?xml-stylesheet href="perl1.css" type="text/css"?>
                    $1                                   $2
 |--------------------------------------------|          |
<link href="//www.perl.org/css/perl1.css" rel="stylesheet">
                $1                        $2
 |-----------------------------|          |
<link href="/css/perl.css" rel="stylesheet">