str(rrule.rrulestr('DTSTART:19970105T083000\nRRULE:FREQ=YEARLY;INTERVAL=2;BYMONTH=1;BYDAY=SU;BYHOUR=8,9;BYMINUTE=30'))
Gives:
'DTSTART:19970105T083000\nFREQ=YEARLY;INTERVAL=2;BYMONTH=1;BYDAY=SU;BYHOUR=8,9;BYMINUTE=30'

str(rrule.rrule(freq=rrule.DAILY, dtstart=dt.datetime.now(), byweekday=rrule.MO(10), count=10))
Gives:
'DTSTART:20150526T004628\nFREQ=DAILY;COUNT=10;BYDAY=MO'

Notice, that RRULE token is omitted everywhere.

Why? Is it in iCalendar RFC?