Is fractional_seconds_allowed attribute needed in C_DURATION?

In the current spec I have found that attribute in Archetype Object Model 1.4 (AOM1.4)

By looking at the ISO8601 Wikipedia (hope we can look at the spec soon) there is no fractions for the seconds in a duration. If that is correct, then I don’t understand what fractional_seconds_allowed is representing.

Any ideas?