Date.months_in_year

You're seeing just the function months_in_year, go back to Date module for more information.
Link to this function

months_in_year(date)

View Source (since 1.7.0)

Specs

months_in_year(Calendar.date()) :: Calendar.month()

Returns the number of months in the given date year.

Example

iex> Date.months_in_year(~D[1900-01-13])
12