Date.days_in_month

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

days_in_month(date)

View Source (since 1.4.0)

Specs

days_in_month(Calendar.date()) :: Calendar.day()

Returns the number of days in the given date month.

Examples

iex> Date.days_in_month(~D[1900-01-13])
31
iex> Date.days_in_month(~D[1900-02-09])
28
iex> Date.days_in_month(~N[2000-02-20 01:23:45])
29