protected function parseOptional($content)
    {
        $this->typeCheck->parseOptional(func_get_args());

        if (preg_match(static::PATTERN_VARIABLE_LENGTH, $content)) {
            return true;
        }

        return false;
    }
protected function parseOptional($content)
    {
        $this->typeCheck->parseOptional(func_get_args());

        if (preg_match(static::PATTERN_VARIABLE_LENGTH, $content)) {
            return true;
        }

        return false;
    }
@param string $content

@return boolean