ISO week date

ISO weeks defined in ISO 8601 provide an interoperable way to refer to weeks (both for computers and for humans). They aren't that hard to understand, and seem to be used in several parts of the world. For Americans, these can be a little confusing (e.g. weeks start on Monday rather than Sunday), but the benefit is that each weekend has one identifier, rather than two (e.g. the "weekend of 2020W19" comprises May 9th and 10th, the Saturday and Sunday at the end of that week). Since Thursday is in the middle of ISO weeks, Thursdays are used as the anchor for numbering ISO weeks (e.g. 2020W01 has the first Thursday of 2020, which was January 2nd)