public OXmlOpenHeaderElement _Deserialize(BsonReader bsonReader, IBsonSerializationOptions options)
        {
            OXmlOpenHeaderElement element = new OXmlOpenHeaderElement();

            while (true)
            {
                BsonType bsonType = bsonReader.ReadBsonType();
                if (bsonType == BsonType.EndOfDocument)
                {
                    break;
                }
                string name = bsonReader.ReadName();
                switch (name.ToLower())
                {
                case "type":
                    if (bsonType != BsonType.String)
                    {
                        throw new PBException($"wrong type value {bsonType}");
                    }
                    string type = bsonReader.ReadString();
                    //"openfooter"
                    if (type.ToLower() != "openheader")
                    {
                        throw new PBException($"invalid Type {type} when deserialize OXmlOpenHeader");
                    }
                    break;

                case "headertype":
                    if (bsonType == BsonType.Null)
                    {
                        break;
                    }
                    if (bsonType != BsonType.String)
                    {
                        throw new PBException($"wrong HeaderType value {bsonType}");
                    }
                    element.HeaderType = bsonReader.ReadString().zParseEnum <HeaderFooterValues>();
                    break;

                default:
                    //OpenHeaderFooter
                    throw new PBException($"unknow OpenHeader value \"{name}\"");
                }
            }
            return(element);
        }
        public override void Serialize(BsonWriter bsonWriter, Type nominalType, object value, IBsonSerializationOptions options)
        {
            if (value == null)
            {
                throw new PBException("serialize OXmlOpenHeader value is null");
            }
            if (_trace)
            {
                pb.Trace.WriteLine("OXmlOpenHeaderElementSerializer.Serialize()");
            }

            OXmlOpenHeaderElement element = (OXmlOpenHeaderElement)value;

            bsonWriter.WriteStartDocument();
            bsonWriter.WriteString("Type", "OpenHeader");
            bsonWriter.WriteString("HeaderType", element.HeaderType.ToString());
            bsonWriter.WriteEndDocument();
        }