title: Use YAML with variables
body: <p>Are variables within YAML files possible? For example:</p>
  
  <pre><code>theme:
    name: default
    css_path: compiled/themes/$theme.name
    layout_path: themes/$theme.name
  </code></pre>
  
  <p>In this example, how can <code>theme: name: default</code> be used in other settings? What is the syntax?</p>