Interface GetExtendedOptions

What the content edge is read from.

• 'content' — the range's own content, walked from cell. This is Ctrl+Arrow: it runs to the end of the block it is in, or from a blank onto the next block.
• 'adjacent' — the two lines flanking the range on the cross axis (for a downward extension, the column left of the left edge and the column right of the right edge). Each contributes its contiguous run measured from the line the extension would start on, and the further of the two wins; a flank that starts blank contributes nothing, which is why a spacer column stops the extension dead. The reach is then cut short before the nearest populated line inside the range's own columns, so an existing block is not run over. This is the destination Excel picks when the fill handle is double-clicked, and it feeds ICellRange.autoFill directly.

The cell to walk from. Only 'content' extends from a cell — the flanking lines a 'adjacent' extension reads are fixed by the range's own edges — so this is ignored there.

Where a walk that begins on a blank cell comes to rest.

• 'enter' — on the first cell of the block it runs into. This is Ctrl+Arrow.
• 'before' — on the last blank, one short of that block. This is what a double-clicked selection border does.

Blanks are the only thing this changes: from a populated cell both run to the end of that cell's own block and stop in the same place. It is also independent of basis — that says where the boundary is read from, this says what happens on the way — though 'adjacent' has nothing to apply it to, since a blank flank contributes no reach in the first place.