Analysis of information sources in references of the Wikipedia article "Dấu thời gian" in Vietnamese language version.
3.5 Expansion … By mutual agreement of the partners in information interchange, it is permitted to expand the component identifying the calendar year, which is otherwise limited to four digits. This enables reference to dates and times in calendar years outside the range supported by complete representations, i.e. before the start of the year [0000] or after the end of the year [9999].
