Numbers opens the CSV file, gives the user a screen to control import settings, and supports exporting as a CSV with custom delimeters. Excel does save back to

Numbers opens the CSV file, gives the user a screen to control import settings, and supports exporting as a CSV with custom delimeters. Excel does save back to CSV. It discards half your changes because they can't be saved in a CSV, modifies anything that could possibly be a date, and rounds random numbers, THEN it saves it as a CSV. Numbers makes this an explicit "Export" option because silently saving these types of changes is super dangerous.