What is the method to confirm the validity of the date format in fhir?

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The method to confirm the validity of the date format in FHIR is to use the FHIR date/time format specification called ISO 8601. This specifies a standard format for dates and times in a year-month-day format, along with optional time and timezone information. The format should include a year (YYYY), a month (MM), and a day (DD) in that order. The optional time information should include hours (HH), minutes (MM), and seconds (SS) in that order, separated by a colon. The timezone information should be in the format +/-HH:MM or +/-HH. For example, "2021-10-01T08:30:00+02:00" would be a valid FHIR date/time format that represents October 1st, 2021 at 8:30 am in a timezone 2 hours ahead of UTC. Any date or time formats that do not conform to this specification should be considered invalid.