Add specific support for subfeed breakers.

Be able to set the number of subfeed breakers on a panel (similar to how the number of poles is currently set on a panel).

Have the panel schedule update to document which breakers are subfeed. We likely would add a separator block between the branch circuit and subfeed breakers that you could customize. The default block would have a line across the schedule plus some text indicating branch circuit breakers above and subfeed below. You could then modify that as desired for your documentation purposes.