The international standard ISO 8601 "Data elements and interchange formats
- Information interchange - Representation of dates and times" defines
three distinct calendars by which days can be labeled. It also defines
textual formats for the representation of dates in these calendars. This
module provides functions to convert dates between these three calendars
and Chronological Julian Day Numbers, which is a suitable format to do
arithmetic with. It also supplies functions that describe the shape of
these calendars, to assist in calendrical calculations. It also supplies
functions to represent dates textually in the ISO 8601 formats. ISO 8601
also covers time of day and time periods, but this module does nothing
relating to those parts of the standard; this is only about labeling days.
