@albinanigans @nixCraft I recently learned that ISO-8601 is actually extremely broad, allowing for several different date formats. None of them violate year-month-day hierarchy though.

I like using the best overlap between ISO-8601, RFC-3339, and the HTML standard that I can. This page describes the overlap quite nicely. If the diagram at the top isn’t accessible, there’s a table at the bottom.

YYYY-MM-DD is the only date format that’s valid across all three standards, but there are too many valid Date-Time formats IMO.