title: QML: Component vs Item as a container
body: <p>What is the difference between <code>Component</code> and <code>Item</code> in QML ? The documentation is not absolutely clear here. 
  What is the preferred type to use as a container for several widgets?
  Can it be replacable by <code>Rectangle</code>?</p>
  
  <p>For example, what is the difference in the following declarations:</p>
  
  <pre><code>Item {
      id: itemWidget
  
      Rectangle { id: one }
      Rectangle { id: two }
  }
  </code></pre>
  
  <p>and </p>
  
  <pre><code>Component {
      id: componentWidget
  
      Rectangle { id: one }
      Rectangle { id: two }
  }
  </code></pre>
  
  <p>Why do we usually use <code>Component</code> when declaring a <code>delegate</code>?</p>