Dates without years
Not sure if this is true by design but there's no error message if a value of type 'Date' consists of just a day and a month, for instance "2 February" - a query for "2 February" gives appropriate results. Because such incomplete dates cannot be interpreted as points in time, as the page points out, I was surprised to see this behaviour, but if it is a bug, I'd welcome it anyway: it lets you add annual events without any specific start and end.
(Note also that if you had events on, say, 2 February 1567, 2 February 1785 and 2 February 2014, there's no way of querying for all events that happened on 2 February in whatever year; but adding "2 February" as a value would do the trick).
> type 'Date' consists of just a day and a month, for instance "2 February" - a query for "2 February"
Well, it is conceivable that a user would interpret "2 February" as something like 2nd of Feb with NO YEAR but the system understands the input as 0002 Year + 2nd Month hence the point in time is fixed by (Calendar model 2 (JL)/2 (Year) / 2(Month)) without a specific day or time.
From that perspective, Year + Month are allowed to exists without having to specify a day or time.