protected function bindPartConcat($var, ServerRequestInterface $request, array $parts, &$part)
    {
        if (!is_string($var) || $var[0] !== '~' || substr($var, -1) !== '~') {
            return false;
        }
        
        $pieces = array_map('trim', explode('~', substr($var, 1, -1)));
        $bound = array_filter($this->bind($pieces, $request, $parts));
        $part = [join('', $bound)];
        
        return true;
    }