Very confusing.
DateTimeFormat
- Format sting - %y is 2-digit year, %Y is a 4-digit year. How about yy or yyyy. Much easier to remember and consistent with other tools like Excel.
DateTimeDiff
- Format string - 'year' but above function year is referenced as %y ?? Too easy to mix this up.
Also, documentation is limited. Give a separate page for each function and an overview to discuss date handling.