title: mongoose.js 3: how to tell that nested is not a document
body: <p>My mongoose Schema:</p>
  
  <pre><code>mongoose.Schema({
          title: 'string',
          items: [{
              uid: 'string',
              type: {type: 'string'},
              title: 'string',
              items: [{uid: 'string', type: {type: 'string'}, text: 'string'}]
          }]
      });
  </code></pre>
  
  <p>How to tell mongoose that items (and items of items) are not documents, but just nested objects? I need neither the <code>_id</code> property nor any document's functionality for them, but I want to define them and restrict with schema.</p>
  
  <p>Is <code>_id: false</code> is enough?</p>