TODO list for Perl module DateTime::Event::Recurrence

* new frequencies (in order to add support to missing DT::E::ICal recurrences):
  - yearly_week with other week-start-days (rfc2445 WKST style)
  - yearly_week starting in first weekday of year (rfc2445 1FR style)

    week_start_day => 'mo'   -- yearly 
    week_start_day => '1mo'  -- yearly and monthly 

  - add tests with 'interval' > 1
  - add 'previous' tests

* start parameter
  - is it just for synchronizing the interval?
  - interval extends to before 'start' (current implementation)
  - other options:
    Span start
    DTSTART meaning

* find out how it behaves with mixed timezones

* more tests for invalid month-day

* allow interleaved neg/positive values
    my $month = monthly DateTime::Event::Recurrence (
        days => [ -1, 31, 15 ],
        minutes => [ 30 ] );


* interval
  - finish tests for offset (base-date)
  - test it near DST changes
  - should not use {local_rd_days} directly
  - POD

* add more argument overflow tests:
  day in year, 
  week in year, 
  negative values, 
  ... 

