Defines a new undo element format (fun . args), which means “undo by applying fun to args”. For spreadsheet buffers, it allows undos in the data area even though that’s outside the narrowing.
When copying from the print area of a spreadsheet, treat the region as a rectangle and attach each cell’s formula and printer as ’ses properties.
When yanking into the print area of a spreadsheet, first try to yank as cells (if the yank text has ’ses properties), then as tab-separated formulas, then (if all else fails) as a single formula for the current cell.