title: Does the ES7 decorator spec require descriptors to have an `initializer` method
body: <p>Using Babel to transpile the following es7 code:</p>
  
  <pre><code>let obj = {
    @decorate
    prop: 10
  }
  
  let decorate = ( object, propertyName, desc ) =&gt; desc
  </code></pre>
  
  <p>When <code>decorate</code> is called, the property descriptor <code>desc</code> contains a method named <code>initializer</code>, that returns the value of <code>obj.prop</code> when executed.</p>
  
  <p>Is the <code>initializer</code> method part of the es7 Decorator specification, or is this purely a side effect of Babel converting to es5?</p>