Date-Set TODO 
(Some items apply to Set::Infinite)

EXCLUDE

    exclude might have problems applying an unbounded recurrence to another unbounded recurrence

RRULE

	should not backtrack if it can solve the problem using COUNT

	where do "DUE" belong?

	TZ ?

SYNTAX

	'iterate' options 'no-sort', 'no-merge', 'keep-null' ...

	extra: wrappers (like: weekday('thursday') )
	some tough cases: yearweek(10) monthweek(2)
	-- partly done: ICalSet.pm

	'select' switch for negative-index overflow behaviour (end of subset, or end of freq)
	tests: add test for negative 'by'

	negative values in select should count backwards from end
	-- test! insert debug -- ical.pl 134 should show 2001-09-30

	remove 'interval' option from select

	old: correct syntax problems due to accepting ( [ 1 .. 10 ] ) as input - see POD.

	make 'freq' work with 'days', etc.

	extra: make offset accept ICal times

	extra: offset option "middle"

	extra: "indexes" filter to help dealing with sparse lists:
	(,,10,,12,,14,,,)->indexes gives (2,4,6)

	extra: Make a 'strict' option for "quantize" and other filters, 
	that will intersect
	each unit back to the object, that is:
	Interval:                     [************************]
	Quantized:                [*********)[*********)[*********)
	Quantized->Stricted:          [*****)[*********)[******]

	think about: "push-pop", "dup", "drop" mechanism

	think about: some "if-else" mechanism

TESTS

	test fractional seconds

DOCUMENTATION

	document:
		new method 'compact'
		offset option 'mode=>circle'
		iterate
		no_cleanup

	document '->trace({options})->' method

	document: quantize extensibility through hash-subs

CACHEING

	make a 'flush'-cache method. Make a 'cache-registry'.

	think about: caching for union, etc  

	extra: caching for the filters. 

OTHER

	check for negative-epoch errors (quantize, select, offset).

	remove a lot of debug #-print lines

	internal: it may be good to have a pointer to the "root" object
	in the filters. They already have a "parent" pointer.

	oo: provide a general filter "install" mechanism (quantize, select, etc)
	check: cleanup "type" hack

	old: Make a global mode for `open_*' 

	old: Quantize_Date should care of daylight savings time



