ReadonlydestinationThe cells the fill covers — the range itself, or the destination that was asked about.
ReadonlydirectionWhich way the series runs — the direction asked for, or the one the range's own shape implies.
ReadonlyofferedThe Preset.ids that can be offered, in registry order.
A preset is offered when it applies to ANY line of the range: a column of dates beside a column of numbers offers the date fills, and the numeric column falls back to a copy rather than the entry being greyed for both. WHICH of them a surface lists is its own business — a Series dialog carrying a Trend checkbox leaves the trend presets out.
ReadonlypresetThe Preset.id to open on — what the range's leading line already reads as.
A date series is named at its largest unit (DateSeries), a numeric one is linear,
and text falls to series — reading the series off the template is the best guess text can
be given, and is what makes test 1, test 2 and Jan, Feb fill as series. Only a selection
nothing recognizes falls through to copy, which is the honest answer there.
ReadonlysizeHow many cells deep destination is along direction — the template included.
ReadonlytemplateThe cells the series is read from — the range's leading CONTENTFUL run along direction.
Excel seeds from the first cell alone and overwrites everything after it. Taking the leading
run instead is what lets a template say something: 1, 5 continues 9, 13, 17 where a
one-cell template can only copy. A run covering the whole range would leave nothing to fill,
so it falls back to the first line — which is how a column of values gets renumbered.
Asked with a destination — the fill handle's drag — the template is the whole range as it is, blanks included, because the drag already said what to read.
ReadonlytemplateHow many cells deep template is along direction.
The default fill a selection implies — which cells it would read, which it would cover, the types that can be offered for it, and the one to open on.
See
ICellRange.getDefaultAutoFillCriteria, which answers this for a range.