if (key->empty() || (int) key->length() > key_max_len)

    if (key->empty() ||
        (key_max_len != -1 && (int) key->length() > key_max_len))
    {

            "selector '%s' must be exactly one character in '%s'",
            key->c_str(), s.c_str());

            "selector '%s' must be <= %d characters in '%s'",
            key->c_str(), key_max_len, s.c_str());
    }

    std::string err = mapdef_split_key_item(s, &key, &sep, &arg);

    std::string err = mapdef_split_key_item(s, &key, &sep, &arg, -1);