[petsc-dev] What part of DMPlexProjectFunctionLocal restricts to the boundary in snes ex12?

[Geoffrey Irving]

I'm trying to understand the boundary condition projection function

     DMPlexProjectFunctionLocal

It seems to access the default section of the DM, which knows about
boundary conditions, but doesn't seem to access it in a way that would
use the boundary condition information.  How does it know to only do
work on the boundary?

If it snapped to the "boundary conditions" globally ex12 would still
work since the "boundary conditions" are the globally correct exact
solution, but I imagine that's not actually what's happening.

Thanks,
Geoffrey