I have use case where I need to fill and insert some element before routing to business service.
Tricky part is that I need to insert element between optional elements, so I think neither of insert after/before/first/last will work.
Now how can I insert, lets say <X>999</X> between C and D?
If I would use "after C" and C is missing, then X is not inserted. If I use first or last and any of A-F elements exist, then there is schema validation error at business service. I think of something like finding last existing element of A/B/C. Or something else?