Will Pazner

> `ChildrenInEntity`, there is no children in an entity. There can be children of an entity. I agree, `ChildrenOfEntity` is better. Or just `Children`… > `ParentsTouchedByEntities` looks like a squeezed...

> I'm not convinced on the need of `EntityIDs`. `std::vector` (or `mfem::Array` if it really has to) seems more natural to me. > > IMHO an `EntityID` is unique. That...

@camierjs, you might be interested in the simplifications to the linear form extension possible in 2487dd44be8ed6df95b377cb1a9162b290f07f19.

@artv3, this is ready for you to take a look at and see if it would work for your purposes.

Any thoughts on this proposal? I think it would be good to reach a consensus on a viable design and then work on getting an acceptable implementation and PR ready.

The case of `rho == nullptr` looks like it is definitely handled correctly. For the velocity, it will boil down to the correctness of `QuadratureFunction::ProjectGridFunction`. That being said, the unit...

No, it shouldn't directly affect the use of geometric factors, but there is always the possibility of some unintended consequence that we didn't anticipate. I just bring up the possibility...

The METIS errors have been showing up intermittently in the Windows CI on many (all?) branches. We should get to the bottom of it, but I suspect that it's not...

This PR is now [under review](https://github.com/mfem/mfem/blob/master/CONTRIBUTING.md#pull-requests) (see the table in the PR description). To help with the review process, please **do not force push** to the branch.

@mlstowell, @acfisher, is example 6 expected to fail? Is it a lot of work to get it to run properly? Any idea why ex6p works for that one example but...