Parse error: syntax error, unexpected 'class' (T_CLASS) in /srv/initialnews/scribble/index.php(278) : regexp code on line 1

Fatal error: preg_replace(): Failed evaluating code: "<a class=\"${this.class}__promo-button\" href=\"index.php?page=".$page."&url=" . urlencode(absolute("#openweb-convo", $url)) . "\"" in /srv/initialnews/scribble/index.php on line 278