PHP Problem

class html {
    private static $content;

    public static function a($p) {
        self::$content &= $p."\n";
    }
   
    public static function an($p) {
        if($a->admin) {
            self::$content &= $p."\n";
        }
    }
   
    public static function write() {
        return self::$content;
    }
}

html::a("test");
echo html::write();

0

Why it does not work?

http://www.thewebcomiclist.com/o/8538