Returns the number of days in this month, or zero if the month is not
between 1 and 12.
</item>
+<item tag="unsigned YearDay()">
+Calculate the day of the year, starting from January 1st.
+For example, 1 means January 1st and the 22nd of February is 53.
+If the date is not a proper calendar date, return 0.
+</item>
<item tag="unsigned WeekDay()">
Calculate the day of the week, where 1 is Monday and 7 is Sunday.
If the date is not a proper calendar date, return 0.