protected function multiplySelectors($env) {
        $envs = array();
        while (null !== $env) {
            if (!empty($env->selectors)) {
                $envs[] = $env;
            }
            $env = $env->parent;
        };

        $selectors = array();
        $parentSelectors = array(array());
        while ($env = array_pop($envs)) {
            $selectors = array();
            foreach ($env->selectors as $selector) {
                foreach ($parentSelectors as $parent) {
                    $selectors[] = $this->joinSelectors($parent, $selector);
                }
            }
            $parentSelectors = $selectors;
        }

        return $selectors;
    }