[boost] boost::date_time: ISO compliant IO for periods/durations?

Hello boosters, I would like to know whether there already exist ISO 8086 conforming extractors/inserters for the duration/period classes? Specifically I am looking for io/string functions which can handle "Periods of Time, no Specific Start or End", which begin with a 'P' following a list of periods, e.g. "P18Y9M4DT11H9M8S" (18 years, 9 months, 4 days, 11 hours, 9 minutes and 8 seconds) (I am using the term period in the sense ISO 8086 seems to do, i.e. including durations and periods - or did I overlook something?) Thanks for any help, Daniel