Why doesn't Mongo use the ISO-8601 standard for formatting dates? This affects both the $week and $dayOfWeek operators. It's very frustrating to have to hack in a bunch of $if operators to make Mongo conform to the only real standard for dates in popular usage.

Right now Mongo returns $dayOfWeek as 1 = Sunday and 7 = Saturday, but the ISO-8601 standard is 1 = Monday and 7 = Sunday.

And now Mongo uses the %U operator from C, when you should use the %V operator as this is the universal standard.

The world has moved to ISO-8601. MongoDB should catch up!