Ah! It's ok. I see. I had effectively already done this, and was getting confused by trying to re-use a single formpage. However, I was collecting the entire includelet spec in a formfield. I can't then reasonably expect to be able to substitute another @value@ into the result of an already substituted @formfield@! This would require nested substitutions within a single ::xowiki::Form!! 😱
If I put the fixed part of the includelet declaration into the ::xowiki::Form spec, then I see that I could add a hidden field to the form and pass in values using a query parameter in the url. The disadvantage with this is that then I would lose the ability to add SEO content to the resulting carousel page, which has other fields specifically for this purpose, and any case, to drive a menu you would have to have an instance of one form or the other for each folder of pictures.
I apologise that this may be a bit confusing to read, but I have posted it as a record for future reference.
R.
