private string WriteProductMix(XmlWriter writer, ProductMix productMix)
{
var productId = productMix.Id.FindIsoId() ?? GenerateId();
TaskWriter.Ids.Add(productId, productMix.Id);
writer.WriteStartElement(XmlPrefix);
writer.WriteAttributeString("A", productId);
writer.WriteAttributeString("B", productMix.Description);
writer.WriteAttributeString("F", "2");
WriteTotalQuantity(writer, productMix.TotalQuantity);
WriteProductComponents(writer, productMix.ProductComponents);
writer.WriteEndElement();
return productId;
}