xs:duration - an ISO 8601 duration

• The syntax is PnYnMnDTnHnMnS where each 'n' is a number.

• Y - years, M - months, D - days, H - hours, M - minutes, S - seconds.

• A minus sign prefix signifies a "negatuve duration".

• You can omit fields but if you mix years, months, or days with times, you need the 'T' separator.

• You need the 'T' to signify time periods.

Examples:

• 1 month: P1M

• 2 days, 3 hours: P2DT3H

• 30 months: P30M

• 30 minutes: PT30M

• 1 hour 30 minutes: PT1H30M

• See answers.com for more information on ISO 8601.