[ENH] Allow fractional seconds in scans file datetimes

src/03-modality-agnostic-files.md

@@ -264,15 +264,16 @@ imaging acquisition sequence (each run `.nii[.gz]` file) within one session.
 Each `.nii[.gz]` file should be described by at most one row. Relative paths to
 files should be used under a compulsory `filename` header. If acquisition time
 is included it should be under `acq_time` header. Datetime should be expressed
-in the following format `2009-06-15T13:45:30` (year, month, day, hour (24h),
-minute, second; this is equivalent to the RFC3339 "date-time" format, time zone
-is always assumed as local time). For anonymization purposes all dates within
-one subject should be shifted by a randomly chosen (but common across all runs
-etc.) number of days. This way relative timing would be preserved, but chances
-of identifying a person based on the date and time of their scan would be
-decreased. Dates that are shifted for anonymization purposes should be set to a
-year 1925 or earlier to clearly distinguish them from unmodified data. Shifting
-dates is RECOMMENDED, but not required.
+in the following format `2009-06-15T13:45:30[.000000]` (year, month, day,
+hour [24h], minute, second, and optionally fractional second; this is
+equivalent to the RFC3339 "date-time" format, time zone is always assumed as
+local time). For anonymization purposes all dates within one subject should be
+shifted by a randomly chosen (but common across all runs etc.) number of days.
+This way relative timing would be preserved, but chances of identifying a
+person based on the date and time of their scan would be decreased. Dates that
+are shifted for anonymization purposes should be set to a year 1925 or earlier
+to clearly distinguish them from unmodified data. Shifting dates is
+RECOMMENDED, but not required.
 
 Additional fields can include external behavioral measures relevant to the
 scan. For example vigilance questionnaire score administered after a resting