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| situation | encoding format | example - encoded | example - display | notes |
|---|---|---|---|---|
| year known | yyyy | 1989 | 1989 | |
| year and month known | yyyy-mm | 1989-03 | March 1989 | |
| year, month, and day known | yyyy-mm-dd | 1989-03-22 | March 22, 1989 | |
| year given is uncertain | yyyy? | 1989? | 1989? | The "?" character may occur only at the end of the date string and apply to the entire date. |
| year and month given are uncertain | yyyy-mm? | 1989-03? | March 1989? | The "?" character may occur only at the end of the date string and apply to the entire date. |
| year, month, and day given are uncertain | yyyy-mm-dd? | 1989-03-22? | March 22, 1989? | The "?" character may occur only at the end of the date string and apply to the entire date. |
| year given is approximate | yyyy~ | 1989~ | circa 1989 | The "~" character may occur only at the end of the date string and apply to the entire date. |
| year and month given are approximate | yyyy-mm~ | 1989-03~ | circa March 1989 | The "~" character may occur only at the end of the date string and apply to the entire date. |
| year, month, and day given are approximate | yyyy-mm-dd~ | 1989-03-22~ | circa March 22, 1989 | The "~" character may occur only at the end of the date string and apply to the entire date. |
| date range is known | yyyy/yyyy | 1989/2019 | 1989 to 2019 | Also works with YYYY-MM and YYYY-MM-DD W3C formats (e.g. "1989-03-22/2019-08-14") |
| date range is approximate or uncertain | yyyy-mm~/yyyy-mm?mm~ | 1989-03~/2019-08~ | circa March 1989 to August 2019 | Also works with "?" character. |
| general time period is known but the specific year or decade is unspecified | yyyX | 198X | 1980s | Also works at a century level (e.g. "19XX" = "1900s") |
| date range where the beginning and end dates are known but specific years and decades are unspecified | yyyX/yyXX | 198X/20XX | 1980s to 2000s | Does not work with yyyy-mm and yyyy-mm-dd formats |
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