Month is not always string array, for example in ISO: 2020-11-23.
And days can be string as well: "1st November".
And days can be string as well: "1st November".
If we go all the way back, one could say it was a mixed array of string and integer. September (7), October (8), November (9), and December (10) are linguistically ordinal names... but they’re all off by two since the deprecation of the Roman calendar.
(written 4 Freezy 229)
March (1) April (2) May (3) ... July (5) (named after Julius Caesar) August (6) (named after Augustus) September (7) ... etc.
The reason being in the ancient world all serious activity begins in the spring, especially war campaigns which were to be under the aegis of the god Mars, from which the name of the month.
Note that when we have a leap year we add the extra day to the end of the Roman year, that is at the end of February which is the last month of the year.
More precisely, we duplicate the sixth of the calends of March. This is why in French the leap year is called 'bisextile'.