What changed between two readings, as appends where every layer that
changed grew by one new bar at its end.
A layer that grew by one bar is an append even when the bar before it was
revised too, as a feed does when it closes one bar and opens the next in
the same message; the revision then goes into AppendPlan.base, set
silently first, so the new bar is still the one announced.
The plan; null when no layer grew by one bar and something else
changed -- a revised bar alone, a reload, a series added -- and the figure
is to be replaced
What changed between two readings, as appends where every layer that changed grew by one new bar at its end.
A layer that grew by one bar is an append even when the bar before it was revised too, as a feed does when it closes one bar and opens the next in the same message; the revision then goes into AppendPlan.base, set silently first, so the new bar is still the one announced.