title: How to query documents in docpad based on arrays of objects
body: <p>I have DocPad documents that look like this:</p>
  
  <pre><code>---
  categories: [{slug: ""}, {slug: ""}, ...]
  ---
  
  Document content.
  </code></pre>
  
  <p>How can I query all documents which have a predefined slug value in the <code>meta.category</code> array?</p>