title: Use placeholders in yaml
body: <p>Is there a way to use placeholders in yaml like this: </p>
  
  <pre><code>foo: &amp;FOO
      &lt;&lt;propname&gt;&gt;: 
          type: number 
          default: &lt;&lt;default&gt;&gt;
  
  bar:
      - *FOO 
         propname: "some_prop"
         default: "some default" 
  </code></pre>