Recurrency notation RFC-5545
I learn about the https://datatracker.ietf.org/doc/html/rfc5545
From the specification:
This document defines the iCalendar data format for representing and exchanging calendaring and scheduling information such as events, to-dos, journal entries, and free/busy information, independent of any particular calendar service or protocol.
really interesting RFC, it defines recurrency with a machine parseable string so we can defien something like every Friday for 6 times using a standard notation:
RRULE:FREQ=WEEKLY;BYDAY=FR;COUNT=6
And, of course, there are libraries already for that: