Description:
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A DateInterval object can represent negative intervals, when its $invert property equals 1.

However, there's no way (or no documented way) to construct a DateInterval object that is inverted with the constructor.

Yoy need to do:
  $interval = new DateInterval("whatever"); 
  $interval->inverted = 1;

It's absolutely ridiculous and pathetic that there exist values that can be represented by the class but cannot be created with the constructor.


The interval_spec should support a way to specify inverted intervals.
Any of these would be fine, it's just a matter of taste:
- prefix the interval with a "-" (minus) sign
  e.g. "-P1Y3D"
- a "-" (minus) sign after the initial P
  e.g. "P-1Y3D"
- some suffix at the end, for example "I" for "Inverted"
  e.g. "P1Y3DN"