Durations:
dur-second = 1*DIGIT "S"
dur-minute = 1*DIGIT "M" [dur-second]
dur-hour = 1*DIGIT "H" [dur-minute]
dur-time = "T" (dur-hour / dur-minute / dur-second)
dur-day = 1*DIGIT "D"
dur-week = 1*DIGIT "W"
dur-month = 1*DIGIT "M" [dur-day]
dur-year = 1*DIGIT "Y" [dur-month]
dur-date = (dur-day / dur-month / dur-year) [dur-time]
duration = "P" (dur-date / dur-time / dur-week)
Klyne, et. al. Standards Track [Page 13]
RFC 3339 Date and Time on the Internet: Timestamps July 2002
Periods:
period-explicit = iso-date-time "/" iso-date-time
period-start = iso-date-time "/" duration
period-end = duration "/" iso-date-time
period = period-explicit / period-start / period-end
