GERRY ASHTON <[log in to unmask]>:
> For example, would 2017-08-05T-04:00 be valid?
The standard does not consider the case of a zero-length time in combined date-time representations, but it is not incompatible with any format, so it would be a valid extension if the partners in information exchange agreed upon it.
Similarly, decimal floating point formats are only specified for the seconds, minutes and hours fields, although they would also make sense for whole days (or even the other date fields), i.e. 2017-08-05T12:00:00 would be: