Duration: Missing fractional values for components other than seconds

[WORMSS]

Wikipedia ISO 8601#Durations

The smallest value used may also have a decimal fraction,[35] as in "P0.5Y" to indicate half a year.

loc.gov datetime isco 4.4.3.2.b

If necessary for a particular application, the lowest order components may have a decimal fraction.
The decimal fraction shall be divided from the integer part by the decimal sign specified in
ISO 31-0, i.e. the comma [,] or full stop [.]. Of these, the comma is the preferred sign. The decimal
fraction shall at least have one digit, the maximum number of digits in the decimal component
needs to be agreed by the partners in information interchange. If the magnitude of the number is
less than unity, the decimal sign shall be preceded by a zero (see ISO 31-0).