Ahhh, that sounds useful. @MKleusberg does this look good to merge? It's a three-liner. 😄

Thanks, @MyRoGeertGit for contributing this 😄
I have one small suggestion before merging: can we change the datetime() function to just a date() call? Because as far as I see it's just the date which is stored in the number anyway, so the time part of the string would always be 00:00:00.

@MKleusberg
The fractional part of DATE is the hour/min/sec representation.
eg.: 42372.4709375 represents 2016-01-03 11:18:09.
I propose to add both a date and a datetime format.
date ('1899-12-30', Date || " days" )
would indeed be shown as
2016-01-03.

Oh I see. I missed the 'double' bit in your original post. Sorry! This way datetime() does seem like the correct function to use 😄 date() might not even be needed then...
Thanks a lot for your pull request and for the explanation - I haven't used this date format before but am happy to see that DB4S and the display format feature is used in all sorts of ways 😄