protected function parseRuleString($ruleString)
    {
        // Remove at-rule name and unnecessary white-spaces
        $ruleString = preg_replace('/^[ \r\n\t\f]*@page[ \r\n\t\f]*/i', '', $ruleString);
        $ruleString = trim($ruleString, " \r\n\t\f");

        // Extract query list and create a rule from it
        $pageSelector = new PageSelector($ruleString, $this->getStyleSheet());
        $this->setSelector($pageSelector);
    }