Date input fields in forms are initially hidden to not clutter the interface. You can reveal them with clicking on "Show" beside the "Date" label.
To manage uncertainty in time up to 4 dates can be used: a timespan for the beginning and a timespan for the ending.
For example if you knew the exact birth of an actor you could enter 1356 12 23 in the first row, check the birth checkbox (otherwise it would mean first appearance) and add a comment e.g. "It was a good day to be born".
If you are unsure e.g when a Church was destroyed you could use both end dates (chose a wide enough span where you are sure it had happened), enter in the first end year: 1800, in the second end year: 1900.
The application will fill missing days or month with 1 so you would have created the time span 1800-01-01 to 1900-01-01.
|Year||from -3713 to 9999 but not zero|
|Month||from 1 to 12|
|Day||from 1 to 31|
|Comment||a free text field available for begin and end for additional information|
Additionally there are checkboxes for persons to choose if a date (or timespan) is the birth/death (checked) or the first/last appearance (unchecked).
Dates will be validated in the backend so you can just try if you aren't sure about a leap year or something like that.
Most limitations come from PostgreSQL (the database) which in turn uses the Proleptic Gregorian calendar . Thats why there is no year zero (one year before year 1 is the year 1 BC).