ISO 8601:2004 formats

Dates should be in one of the following formats:

• YYYY
• YYYY-MM
• YYYY-MM-DD
• YYYY-MM-DDThhZ
• YYYY-MM-DDThh:mmZ
• YYYY-MM-DDThh:mm:ssZ

where:

• Y is a year digit
• M is a month digit from 01 to 12
• D is a day digit from 01 to 31
• h is an hour digit, from 00 to 23
• m is a minute digit, from 00 to 59
• s is a minute digit, from 00 to 59
• T and Z are the literal uppercase letters "T" and "Z"

To validate a "date and time of day" representation, the following regular expression is sufficient:

^[0-9]{4}((-[0-9]{2}){0,2}|(-[0-9]{2}){2}(T[0-9]{2}(:[0-9]{2}(:[0-9]{2})?)?Z)?)$