public function import(array $arr, $prefix = null)
    {
        $imports = [];
        foreach ($arr as $key => $node) {
            if (strpos($key, 'import') === 0) {
                $mode = substr($key, 7);
                if ($mode == '' || $mode == $this->mode) {
                    $imports = array_merge($imports, $node);
                }

                continue;
            }

            $this->storage[$key] = $this->merge($this->storage[$key], $this->applyPrefix($node, $prefix));
        }

        foreach ($imports as $node) {
            $this->import($node, $prefix);

        }

        return $this;
    }