FluidTYPO3\Vhs\ViewHelpers\Iterator\ExtractViewHelper::flattenArray PHP Method

    public function flattenArray(array $content, $flattened = null)
    {
        foreach ($content as $sub) {
            if (true === is_array($sub)) {
                $flattened = $this->flattenArray($sub, $flattened);
            } else {
                $flattened[] = $sub;
            }
        }
        return $flattened;
    }