Supports import/export for a number of datetime string standards and R datetime classes often including lossless re-export of any original reduced precision including 'ISO 8601' < https://en.wikipedia.org/wiki/ISO_8601> and 'pdfmark' < https://opensource.adobe.com/dc-acrobat-sdk-docs/library/pdfmark/> datetime strings. Supports local/global datetimes with optional UTC offsets and/or (possibly heterogeneous) time zones with up to nanosecond precision.