They are covered in dune-perftool-hyperbolic

The indexing information needs to be stored and reset
for visiting of the second branch.

After a lot of experimenting and stuff...

not in CMakeLists.txt

It obviously is.

Code does not generate so far...

Even if the basis scalar, it is worth to put a shape of (n, 1),
because that is how PDELab thinks about it. Not doing so can have
you end up with mismatches between `Dune::FieldVector<double, 1>` and `double`.