title: Why put type_of_element#id in CSS?
body: <p>Why would you want to do:</p>
  
  <pre><code>h1#chapter1 { text-align: center }
  </code></pre>
  
  <p>Instead of</p>
  
  <pre><code>#chapter1 { text-align: center }
  </code></pre>
  
  <p>If an id is supposed to be unique in a document tree?</p>