title: Document tree is the same as DOM?
body: <p>Here is the sentence</p>
  
  <blockquote>
    <p>The pseudo-class concept is introduced to permit selection based on
    information that lies outside of the document tree or that cannot be
    expressed using the other simple selectors.</p>
  </blockquote>
  
  <p>from <a href="http://www.w3.org/TR/selectors/#pseudo-classes">http://www.w3.org/TR/selectors/#pseudo-classes</a></p>
  
  <p>Is "document tree" have the same meaning as DOM or it's something else?</p>