Function placeholderFromCell

placeholderFromCell(cell: ICell | null): string | null
The ghost formula for a spilled-INTO cell: the spill anchor's formula, as Excel greys it in the formula bar. null for every other cell (including the anchor itself, which owns the formula and so shows it as real text via editStringFromCell).
Parameters
- cell: ICell | null
Returns string | null

Remarks
This is the other half of a deliberate SDK contract: ICell.getText blanks a spill-overflow cell and getFormulaText returns null there (the formula lives only on the anchor), so editStringFromCell yields '' — leaving the field empty for this ghost to fill. Host-called, not called by the input; see SheetCellInputProps.placeholder for why the grid editor must not use it.