Implement easter_day() in recalender

i am currently making my own callender with the link below:

klimeryk/recalendar: ReCalendar - highly customizable calendar for ReMarkable tablets (github.com)

When implementing hollidays from te netherlands i came across a problem the easter days end the days linked to this are depending on the moon.

There is a function in the language(PHP) in whitch recallendar is written called easter_day()

but i don’t know how to implement it in this code this is wat i came up with

’easter(self::YEAR)’ => [ ‘pasen’ ], this function located in the local.config.php file
like ‘4-4’ => [ ‘pasen’ ],

if someone could help would be great!!!