The menu closed without choosing — the drag is over and nothing is filled.
The grid keeps the drag's dashed preview up while a choice is pending, since it shows which cells the menu is about; this is what lets it go. A no-op once fill or series was called — those settle the drag themselves, the dialog included — so a menu can call it from every close path without caring which one it was.
ReadonlydestinationThe cells the fill covers, the template included — where the handle was released.
ReadonlydirectionWhich way the drag went.
Run the chosen fill and select the destination, as a left-drag would. A refused fill (a merge the destination cannot hold) is reported, not thrown.
ReadonlyofferedThe IAutoFill.Preset.ids that can be offered for the template, in registry order — see IAutoFill.DefaultCriteria.offered. Empty for a template with nothing in it.
Open the Series dialog on the drag's template, destination and direction.
ReadonlytemplateThe cells the fill reads — the selection the handle was dragged from.
Everything the fill menu — the right-drag of the fill handle — needs to offer and run a fill.
Remarks
The drag has already decided what is read, what is covered and which way, so unlike FillSeries nothing here is asked per direction. The menu is presentation: it lists the entries it wants in the order it wants, greys those not in
offered, and calls back.