title: Negative DateInterval
body: <p>I want to create a DatePeriod object with a negative DateInterval.</p>
  
  <p>This creates a DatePeriod with the year increasing from today to 2016.</p>
  
  <pre><code>$this-&gt;Set('dates', new DatePeriod(new DateTime(), new DateInterval('P1Y'), new DateTime('2016-06-06')));
  </code></pre>
  
  <p>I want to start at 2016, and using a negative DateInterval move towards todays year</p>
  
  <p>Something like this might illustrate my desire</p>
  
  <pre><code>$this-&gt;Set('dates', new DatePeriod(new DateTime('2016-06-06'), new DateInterval('-P1Y'), new DateTime()));
  </code></pre>
  
  <p>I just can't find any extended info on either DatePeriod or DateInterval on how to do this. All i find is that DateInterval can be inverted.</p>