anchor.diff:  
   -record(m1,{a}).
   
  +skipping_unknown_varint_field_test() ->
  +    #m1{a = undefined} =
  +        decode_msg(<<32,150,1>>, %% field number 4 (not known), wire type = 0
  +                   m1,
  +                   [{{msg,m1}, [#field{name=a, fnum=1, rnum=#m1.a, type=int32,
  +                                       occurrence=optional, opts=[]}]}]).
  +
  +skipping_unknown_length_delimited_field_test() ->
  +    #m1{a = undefined} =
  +        decode_msg(<<34,1,1>>, %% field number 4 (not known), wire type = 2
  +                   m1,
  +                   [{{msg,m1}, [#field{name=a, fnum=1, rnum=#m1.a, type=int32,
  +                                       occurrence=optional, opts=[]}]}]).
  +
  +skipping_unknown_64bit_field_test() ->
  +    #m1{a = undefined} =
  +        decode_msg(<<33,0,0,0,0,0,0,0,0>>, %% field number 4, wire type = 1
  +                   m1,
  +                   [{{msg,m1}, [#field{name=a, fnum=1, rnum=#m1.a, type=int32,
  +                                       occurrence=optional, opts=[]}]}]).
  +skipping_unknown_32bit_field_test() ->
  +    #m1{a = undefined} =
  +        decode_msg(<<37,0,0,0,0>>, %% field number 4, wire type = 5
  +                   m1,
  +                   [{{msg,m1}, [#field{name=a, fnum=1, rnum=#m1.a, type=int32,
  +                                       occurrence=optional, opts=[]}]}]).
  +
   decode_msg_simple_occurrence_test() ->
       #m1{a = undefined} =
           decode_msg(<<>>,
  
positive.code:             Rest;
          length_delimited ->
              {Len, Rest} = decode_varint(Bin),
              <<_:Len/binary, Rest2>> = Rest,
              Rest2;
          bits32 ->
              <<_:32, Rest/binary>> = Bin,
  
negative.code:     case lists:keyfind(FieldNum, #field.fnum, MsgDef) of
          false ->
              Rest2 = skip_field(Rest, WireType),
              decode_field(Rest2, MsgDef, MsgDefs, Msg);
          #field{type = FieldType, rnum=RNum, opts=Opts} = FieldDef ->
              case proplists:get_bool(packed, Opts) of
                  true ->
  