This is a totally inconsequential follow-up to @arnoldkk13 's #6804.

It's all just comments, plus one minor change: The only thing I switched was to list operations first on velocities then on pressures, rather than the other way around, since that's how we often think as the ordering. That isn't @arnoldkk13's fault: It was pressure-first-velocity-second already before #6804, but I think it makes the code easier to read if we follow the standard ordering.