This field is optional.
|Field Name||Date Modified|
|Definition||Date on which the resource was changed.|
This may be used to distinguish among versions of a resource when multiple versions have been made available.
Follow W3C-DTF standard (ISO 8601) of YYYY-MM-DD.
Use only as much of the date as is known.
Use a question mark to show a date is approximate or a circa date.
Use dashes to indicate uncertainty within a decade or a century.
Do not use "Unknown"--just leave the field blank.For a range of dates, put a dash in between dates.