A calendar date item specifies a day of the year. It is specified differently, depending on whether the month is specified numerically or literally. All these strings specify the same calendar date:
2020-07-20 # ISO 8601. 20-7-20 # Assume 19xx for 69 through 99, # 20xx for 00 through 68 (not recommended). 7/20/2020 # Common U.S. writing. 20 July 2020 20 Jul 2020 # Three-letter abbreviations always allowed. Jul 20, 2020 20-jul-2020 20jul2020
The year can also be omitted. In this case, the last specified year is used, or the current year if none. For example:
7/20 jul 20
Here are the rules.
For numeric months, the ISO 8601 format ‘year-month-day’ is allowed, where year is any positive number, month is a number between 01 and 12, and day is a number between 01 and 31. A leading zero must be present if a number is less than ten. If year is 68 or smaller, then 2000 is added to it; otherwise, if year is less than 100, then 1900 is added to it. The construct ‘month/day/year’, popular in the United States, is accepted. Also ‘month/day’, omitting the year.
Literal months may be spelled out in full: ‘January’, ‘February’, ‘March’, ‘April’, ‘May’, ‘June’, ‘July’, ‘August’, ‘September’, ‘October’, ‘November’ or ‘December’. Literal months may be abbreviated to their first three letters, possibly followed by an abbreviating dot. It is also permitted to write ‘Sept’ instead of ‘September’.
When months are written literally, the calendar date may be given as any of the following:
day month year day month month day year day-month-year
Or, omitting the year: