Which way the series runs through the selection. Always Down or Right from a selection.
IAutoFill.Preset.id of the chosen fill type.
OptionalstepIAutoFill.Options.stepValue — meaningless, and hidden, unless the type declares it.
OptionalstopIAutoFill.Options.stopValue
OptionaltrendFit the series to the values rather than stepping from them.
What the Series dialog produces — a IAutoFill.Preset named by id, the direction it runs, and the fields the chosen type declares.
Remarks
The preset is named rather than passed because this crosses a command boundary: the id survives into a transaction's operation params and back, where a filler instance would not.