message Person {
    required int32 id = 1;
    required string name = 2;
    optional string email = 3;

    extensions 10 to max;
}

message Phone {
    extend Person {
        repeated Phone phones = 10;
    }
    enum PHONE_TYPE {
        MOBILE = 1;
        HOME = 2;
    }
    optional string num = 1;
    optional PHONE_TYPE type = 2;
}