Enter a date or date-range in (non-canonical) datetime format. (I finalized the app before they finalized datetime format, and so my method for encoding durations is non-standard.)

For example:

datetimemeaning
2003-03-19March 19, 2003
1776any date in 1776
1969-06/08any date from the first of June, 1969 through the end of August, 1969
1775/1777any date from January 1, 1775 through December 31, 1777
1945-08-06/11-20any date from August 6, 1945 through November 20, 1945
1517/1658any date during the Protestant Reformation