static GvasFormat.UE_Value UE_Value(JsonReader reader, bool skip_start_token = false)
            {
                if (!skip_start_token)
                {
                    reader.AssertReadToken(JsonToken.StartObject);
                }
                string type_string = reader.AssertReadPropertyNameValue <string>(JsonNaming.UE_Value.TypeString);

                // code structure copied from GvasFormat.Serialization.Binary.UE_Property_Reader.Read_UE_Value
                GvasFormat.UE_Value result;
                switch (type_string)
                {
                //
                // non-container
                case UE_Value_TypeString.BoolProperty:
                    bool value_bool = reader.AssertReadPropertyNameValue <bool>(JsonNaming.UE_Value.Value);
                    result = new UE_ <bool>(type_string, value_bool);
                    break;

                case UE_Value_TypeString.ByteProperty:
                    byte value_byte = reader.AssertReadPropertyNameValue <byte>(JsonNaming.UE_Value.Value);
                    result = new UE_ <byte>(type_string, value_byte);
                    break;

                case UE_Value_TypeString.EnumProperty:
                    string enum_type  = reader.AssertReadPropertyNameValue <string>(JsonNaming.UE_Enum.EnumType);
                    string enum_value = reader.AssertReadPropertyNameValue <string>(JsonNaming.UE_Value.Value);
                    result = new UE_Enum(type_string, enum_type, enum_value);
                    break;

                case UE_Value_TypeString.FloatProperty:
                    float value_float = reader.AssertReadPropertyNameValue <float>(JsonNaming.UE_Value.Value);
                    result = new UE_ <float>(type_string, value_float);
                    break;

                case UE_Value_TypeString.IntProperty:
                    int value_int = reader.AssertReadPropertyNameValue <int>(JsonNaming.UE_Value.Value);
                    result = new UE_ <int>(type_string, value_int);
                    break;

                case UE_Value_TypeString.NameProperty:
                    //case UE_ValueTypeString.StrProperty:
                    string value_string = reader.AssertReadPropertyNameValue <string>(JsonNaming.UE_Value.Value);
                    result = new UE_ <string>(type_string, value_string);
                    break;

                //
                // container
                // redirect.
                // UE_Struct ... lots of them are not engine defined, but game author defined.
                case UE_Value_TypeString.StructProperty:
                    string struct_type = reader.AssertReadPropertyNameValue <string>(JsonNaming.UE_Struct.StructTypeString);
                    reader.AssertReadPropertyName(JsonNaming.UE_Value.Value);
                    switch (struct_type)
                    {
                    case UE_Value_TypeString.Struct.Vector:
                    case UE_Value_TypeString.Struct.Rotator:
                        reader.AssertReadToken(JsonToken.StartArray);
                        float x = reader.AssertReadValue <float>();
                        float y = reader.AssertReadValue <float>();
                        float z = reader.AssertReadValue <float>();
                        reader.AssertReadToken(JsonToken.EndArray);
                        result = new UE_Struct_Vector(struct_type, x, y, z);
                        break;

                    case UE_Value_TypeString.Struct.Quat:
                        reader.AssertReadToken(JsonToken.StartArray);
                        float a = reader.AssertReadValue <float>();
                        float b = reader.AssertReadValue <float>();
                        float c = reader.AssertReadValue <float>();
                        float d = reader.AssertReadValue <float>();
                        reader.AssertReadToken(JsonToken.EndArray);
                        result = new UE_Struct_Quat(struct_type, a, b, c, d);
                        break;

                    default:
                        List <UE_Property> property_list = Read.Object_as_PropertyList(reader);
                        result = new UE_Struct_Generic(struct_type, property_list);
                        break;
                    }
                    break;

                case UE_Value_TypeString.ArrayProperty:
                    string item_type = reader.AssertReadPropertyNameValue <string>(JsonNaming.UE_Array.ItemType);
                    reader.AssertReadPropertyNameValue <int>(JsonNaming.UE_Map.Count);
                    List <GvasFormat.UE_Value> item_list;
                    if (item_type == UE_Value_TypeString.StructProperty)
                    {
                        string sa_name               = reader.AssertReadPropertyNameValue <string>(JsonNaming.UE_StructArray.SA_Name);
                        string sa_item_type          = reader.AssertReadPropertyNameValue <string>(JsonNaming.UE_StructArray.SA_ItemType);
                        string sa_struct_type_string = reader.AssertReadPropertyNameValue <string>(JsonNaming.UE_StructArray.SA_StructTypeString);
                        reader.AssertReadPropertyName(JsonNaming.UE_Array.ItemList);
                        item_list = Read.UE_Value_List(reader);
                        result    = new UE_StructArray(type_string, item_type, item_list.Count, item_list.ToArray(), sa_name, sa_item_type, sa_struct_type_string);
                    }
                    else
                    {
                        reader.AssertReadPropertyName(JsonNaming.UE_Array.ItemList);
                        item_list = Read.UE_Value_List(reader);
                        result    = new UE_Array(type_string, item_type, item_list.Count, item_list.ToArray());
                    }
                    break;

                case UE_Value_TypeString.MapProperty:
                    string key_type   = reader.AssertReadPropertyNameValue <string>(JsonNaming.UE_Map.KeyType);
                    string value_type = reader.AssertReadPropertyNameValue <string>(JsonNaming.UE_Map.ValueType);
                    reader.AssertReadPropertyNameValue <int>(JsonNaming.UE_Map.Count);
                    reader.AssertReadPropertyName(JsonNaming.UE_Map.Map);
                    reader.AssertReadToken(JsonToken.StartArray);
                    var map = new List <UE_Map_KeyValuePair>();
                    while (true)
                    {
                        var token = reader.AssertRead();
                        if (token == JsonToken.StartObject)
                        {
                            reader.AssertReadPropertyName(JsonNaming.UE_Map_KeyValuePair.Key);
                            UE_Value key = Read.UE_Value(reader);
                            reader.AssertReadPropertyName(JsonNaming.UE_Map_KeyValuePair.Value);
                            UE_Value value = Read.UE_Value(reader);
                            reader.AssertReadToken(JsonToken.EndObject);
                            UE_Map_KeyValuePair kvp = new UE_Map_KeyValuePair(key, value);
                            map.Add(kvp);
                        }
                        else if (token == JsonToken.EndArray)
                        {
                            break;
                        }
                        else
                        {
                            throw new FormatException();
                        }
                    }
                    result = new UE_Map(type_string, key_type, value_type, map.Count, map);
                    break;

                default:
                    throw new FormatException($"Unknown value type `{type_string}`.");
                }
                reader.AssertReadToken(JsonToken.EndObject);
                return(result);
            }