This ISO format permits any number of digits after the decimal point in the seconds field. For example 1996-01-30T13:30:00.000000Z is a valid time string to microsecond accuracy. The trailing `Z' is retained as an end delimiter for this purpose.
This format is itself robust for arbitrary timing accuracy, but software developers must take care to ensure that internal formats retain the requisite accuracy.
Users should be aware that some software, for example utilities for handling CDF data files, may be unable to handle timing accuracy greater than milliseconds. This results from the physical limitation of the CDF epoch data type and associated software. Note also that even at millisecond accuracy conversion between the cdf native epoch stored as a double and an ISO time string can result in a 1 msec error.