public function setEncoding($encoding)
    {
        $encoding = trim($encoding);
        if ($encoding !== '') {
            $this->flags .= " --default-encoding $encoding";
        } else {
            $this->flags = str_replace(
                ' --default-encoding ' . $this->encoding,
                '',
                $this->flags
            );
        }
        $this->encoding = $encoding;
    }