title: HuggableInterface in PHP and PSR-8
body: <p>On the <a href="http://www.php-fig.org/psr/">PHP Framework Interop Group site</a> (the maintainer of PSRs), there is a draft <a href="https://github.com/php-fig/fig-standards/blob/master/proposed/psr-8-hug/psr-8-hug.md">PSR-8 Huggable Interface</a>:</p>
  
  <pre><code>namespace Psr\Hug;
  
  /**
   * Defines a huggable object.
   *
   * A huggable object expresses mutual affection with another huggable object.
   */
  interface Huggable
  {
  
      /**
       * Hugs this object.
       *
       * All hugs are mutual. An object that is hugged MUST in turn hug the other
       * object back by calling hug() on the first parameter. All objects MUST
       * implement a mechanism to prevent an infinite loop of hugging.
       *
       * @param Huggable $h
       *   The object that is hugging this object.
       */
      public function hug(Huggable $h);
  }
  </code></pre>
  
  <p>The draft is quite short but does not provide any examples of implementation. What is the purpose of implementing this interface?</p>