difference : 2000 - 1999
result     : -P1Y
difference : 2000-01 - 1999-12
result     : -P1M
difference : 1999-12 - 2000-01
result     : P1M
difference : 1999-12-31 - 2000-01-01
result     : P1D
difference : 1999 - 2000-01
result     : P1Y
difference : 0002-01-05 - 0001-01-04
result     : -P366D
difference : 0002-05-05 - 0001-01
result     : -P1Y4M
difference : -0002-01-05 - 0001-01-04
result     : P729D
difference : 1970-01-01T05:04:03 - 1970-01-01T04:03:02
result     : -PT1H1M1S
difference : 2000-01-01T05:00:03 - 2000-01-01T04:03:02
result     : -PT57M1S
difference : 2000-01-01T05:00:03 - 1980-01-01T04:03:02
result     : -P7305DT57M1S
difference : 1970-01-01T04:03:02 - 1970-01-01T05:04:03
result     : PT1H1M1S
difference : 2000-01-01T04:03:02 - 2000-01-01T05:00:03
result     : PT57M1S
difference : 1980-01-01T04:03:02 - 2000-01-01T05:00:03
result     : P7305DT57M1S
difference : 2002-05-02T23:59:59 - 2002-05-03T00:00:01
result     : PT2S
difference : 2002-05-03T00:00:01 - 2002-05-02T23:59:59
result     : -PT2S
difference : 2000-01-02T05:00:03 - 2000-01-01T04:03:02
result     : -P1DT57M1S