@main[]
^monthdays(2000;1)
^monthdays(2000;2)
^monthdays(2003;1)
^monthdays(2003;2)

@monthdays[year;month]
$from[^date::create($year;$month;1)]
$to[^date::create($from)] ^to.roll[month](+1)
^eval($to-$from)<br>