Year zero
Historians have never included a year zero. This means that between, for example, and , there are 999 years: 500 years BC, and 499 years AD preceding 500. In common usage "anno Domini" 1 is preceded by the year 1 BC, without an intervening year zero. Neither the choice of calendar system (whether Julian or Gregorian) nor the era ("Anno Domini" or Common Era) determines whether a year zero will be used. If writers do not use the convention of their group (historians or astronomers), they must explicitly state whether they include a year 0 in their count of years, otherwise their historical dates will be misunderstood.
Date and time notation in Serbia
Years can be written either with four or two digits, and in the latter case, century is usually replaced with an apostrophe (31. 12. ’06.). Leading zero is rarely used, and in those cases which are considered bad practice, only with months (however it is also optional for the days) (6. 05. 2006.). When literal names of the months are used they are not capitalized, and the four-digit format for the year is always used (31. December 2006). Yet another alternative is to use Roman numerals to indicate the month. In this case a dot is omitted (31. XII 2006).