The cells the fill covers, the template included — where the handle was released.
OptionalnotifierReports a rejected fill, shows the busy state, and opens the Series dialog.
OptionalonThe drag is over: a fill ran, the Series dialog closed, or the menu closed without choosing. Called once — the grid drops the drag's dashed preview here.
The cells the fill reads — the selection the handle was dragged from.
The drag createFillMenu builds a menu for.