title: Does Flutter support negative margin?
body: <p>Negative margin is generally not needed but there are situations where it’s really useful. For example: <a href="https://stackoverflow.com/questions/1840237/why-use-negative-margins">why use negative margins?</a></p>
  
  <p>For now, when I set margin for a container to a negative value, I got the following error:</p>
  
  <pre><code>I/flutter ( 3173): 'package:flutter/src/widgets/container.dart': Failed assertion: line 251: 'margin == null ||
  I/flutter ( 3173): margin.isNonNegative': is not true.
  </code></pre>