ConstReadonlyDisplay: "display"The cell as displayed — number format applied.
ReadonlyValue: "value"The stored scalar — what getValue() returns, with no number format applied.
1234.5678 where display shows $1,234.57, 0.04 where it shows
4%, and a date as its serial. A reader wants one of two things: what the grid shows, or
what a formula computes with. There is deliberately no layer in between — the formula
bar's text (4% at full precision, dates kept) is the stored scalar restyled by the
format's category, and both of those are already reported.
How much formatting to apply before encoding.