Standard format for CIF date and time strings (see
consisting of a yyyy-mm-dd date optionally followed by
the character 'T' followed by a 24-hour clock time,
optionally followed by a signed time-zone offset.
The IUCr standard has been extended to allow for an optional
decimal fraction on the seconds of time.
Time is local time if no time-zone offset is given.
Note that this type extends the mmCIF yyyy-mm-dd type
but does not conform to the mmCIF yyyy-mm-dd:hh:mm
type that uses a ':' in place if the 'T' specified
by the IUCr standard. For reading, both forms should
be accepted, but for writing, only the IUCr form should
For maximal compatibility, the special time zone
indicator 'Z' (for 'zulu') should be accepted on
reading in place of '+00:00' for GMT.