Function edit_text 

pub fn edit_text(wb: &Workbook, sheet: &Sheet, c: CellRef) -> String

What the cell editor and the formula bar start from. Same as Cell::input_text, except that a constant number in a date or time format is shown as a date (as the grid shows it), not as its serial. When the formatted text would not read back as the same date (for example dddd, mmmm d), an ISO yyyy-mm-dd (with hh:mm:ss for a time of day; just hh:mm:ss for a time alone) is used instead, and if even that would not read back, the serial.