Jakob Blomer

@lukasheinrich Having the option of building the container root file system from multiple different sources would be ideal, and it is what we ideally want to see in containerd as...

While we are at it, should we call it `ROOT::RDF::Experimental::FromRNTuple` to avoid confusion with `TNtuple`

@eguiraud Regarding `ROOT::RDF::Experimental::FromNTuple`: looks good to me!

Required flexibility for framework use should be given now by - `RFieldBase::CreateObject()` - `REntry::EmplaceNewValue()`

Root cause may actually be a bug in the `std::variant` field. But needs more investigation.

I cannot reproduce it on Linux, it could be a macOS specific issue.

The PR contains a test that demonstrates that user code can produce empty variants, which the I/O system needs to handle.

Replaced by #15007

One more thought: we may not need to create the model from the first page source. Since we anyway loop through the top-level field descriptors and create the proto fields,...

Sure! This might be a post of itself or a section in larger ROOT7 post/chapter. Let's decide when we know in which form ROOT7 is covered.