docs: public final B host(String host, int port) {
          requireNonNull(host, "host");
          checkArgument(!host.startsWith("group:"), "host: %s (must not start with 'group:')", host);
          checkArgument(port >= 1 && port < 65536, "port: %s (expected: 1 .. 65535)", port);
  
          final InetSocketAddress addr = newEndpoint(host, port);
          checkState(selectedProfile == null, "profile() and host() cannot be used together.");
          hosts = ImmutableSet.<InetSocketAddress>builder().addAll(hosts).add(addr).build();
          return self();
      }