defines the range of values, conforming to the W3C XML Schema Part 2: Datatypes Second Edition specification, expressing a date or a date and a time within the working life of the document.

If it is likely that the value used is to be compared with another, then a time zone indicator should always be included, and only the dateTime representation should be used.

The earliest time expressable with this datatype is 01 January 1970 (the Unix Epoch), which could be written as either 1970-01-01 or 1970-01-01T00:00:00Z.