Can someone explain the last two commands: I understand that r(max) or r(min) is to be used after the summarize command, but what operation is being performed here?

bysort id: gen subid = _n
order id subid
bysort id: egen count_event_days = count(event_window_day)
bysort id: gen max_days_in_window = count_event_days if subid==1
tab max_days_in_window
quietly sum count_event_days
keep if count_event_days==r(max)