[xwiki-users] Conditional transclusion

I have these main documents which I want to consist of a bunch of "subdocuments", which are included/transcluded (own context, so I'll use Display, I guess). Main | -> A | -> B This document has two versions, New and Old: Main_New | -> A_new | -> B_new Main_Old | -> A_old | -> B_old Which is all fine as long as there exists New documents. Now to the finicky part. In some cases, there will be no "new" document for B. I then want this to happen: Main_New | -> A_new | -> B_old Main_Old | -> A_old | -> B_old So, I want the Main document to include a sub-document of it's own type if it exists, and if not, it should pick the "older" document. The selection is based on the "main" documents properties. (Note: I'm having actual new/old documents, so it's not versions of the same document. Also, I have simplified my example a bit, the real case has multiple levels of inclusion. ) Q: How do I go about creating a good conditional inclusion?