Function in boundary condition, defined on boundary only

[dokken]

@mesenev

I would like to be able to manipulate freely with my functions to trace what’s going on. FacetNormal gives Integral of type cell cannot contain a ReferenceNormal outside of the problem formulation scope (I’m sorry if I’m wrong here) so I personally want to avoid to use it.

I have previously posted a recipe on how to project the FacetNormal to an appropriate volume function space, see: How to plot normal unit vector of faces in a 2D mesh? - #2 by dokken
This function would only give you a normal on the boundary, 0 at all other dofs.