message TT1 {
    message T2 {
        message TT3 {
            optional int32 a = 1;
            map<int32, T2> m = 2; 
        }

        required TT3 t3 = 1;
    }

    enum Label {
        LABEL_OPTIONAL      = 1;
        LABEL_REQUIRED      = 2;
        LABEL_REPEATED      = 3;
    };
    
    required T2 t2 = 1;
    required Label t3 = 2;
    required T2.TT3 t4 = 4;
}
