Allow year OR year+month OR year+month+day

I created a forum topic, but no one could help me.

I need a CCK Date field, where the user can type in dates in three different formats:

• 2008
• 09.2008
• 22.09.2008

I tried it, but it always gets automatically corrected to the predefined standard format (current date inserted).

I need it for a chronicle (listing of past events), where some user might only know the year, or year and month or year, month and day.

It should sort the dates as if "2008" would be interpreted (internally) as "00.00.2008" and "09.2008" as "00.09.2008".