The type xsd:duration represents a duration of time expressed as a number of years, months, days, hours, minutes, and seconds. The format of xsd:duration is PnYnMnDTnHnMnS, where P is a literal value that starts the expression, nY is the number of years followed by a literal Y, nM is the number of months followed by a literal M, nD is the number of days followed by a literal D, T is a literal value that separates the date and time, nH is the number of hours followed by a literal H, nM is the number of minutes followed by a literal M, and nS is the number of seconds followed by a literal S. The following rules apply to xsd:duration values:
- Any of these numbers and corresponding designators may be absent if they are equal to 0, but at least one number and designator must appear. 
- The numbers may be any unsigned integer, with the exception of the number of seconds, which may be an unsigned decimal number. 
- If a decimal point appears in the number of seconds, there must be at least one digit after the decimal point. 
- A minus sign may appear before the - Pto specify a negative duration.
 
- If no time items (hour, minute, second) are present, the letter - Tmust not appear.
 
Examples:
- P2Y6M5DT12H35M30S 2 years, 6 months, 5 days, 12 hours, 35 minutes, 30 seconds
- PT20M 20 minutes