I have Julian to Gregorian date conversion popups working for simple dates (@when only). This is not yet on the live site because date ranges are not yet working, but I hope to have them in place soon.

There is a lot of unnecessary conversion between string representations and actual xs:date values all over the code, due to the way it's grown by accretion, and the way we've changed our minds about rendering rules. I should really look at this again, and see if I can take strings on input, convert to xs:date, do all manipulation with xs:date, and then render out right at the end. The problem here is that when we have partial dates (e.g. year-only dates), constructing an xs:date object requires the addition of month and day values, otherwise it fails; this introduces a spurious precision to a date which consists only of a year.