public function copy($from, $to, $fromCopyRef = null)
    {
        $call = 'fileops/copy';
        $params = array(
            'root' => $this->root,
            'from_path' => $this->normalisePath($from),
            'to_path' => $this->normalisePath($to),
        );
        
        if ($fromCopyRef) {
            $params['from_path'] = null;
            $params['from_copy_ref'] = $fromCopyRef;
        }
        
        $response = $this->fetch('POST', self::API_URL, $call, $params);
        return $response;
    }