Added Format → Wrap text, also on the right-click menu for a selection. A wrapped cell breaks its text into lines at the column's edge, and each row is as tall as its tallest wrapped cell. In a wrapped cell, a line break typed with Shift+Enter starts a new line. Unwrap text returns the selected cells to one line.
A merged cell wraps inside its range without making its rows taller. The cell editor now grows to show every line of the text being edited.