<?xml version="1.0"?>
<!-- initially, the default namespace is "books" -->
<book xmlns="urn:loc.gov:books" xmlns:isbn="urn:ISBN:0-395-36341-6">
  <title>Cheaper by the Dozen</title>
  <isbn:number>1568491379</isbn:number>
  <notes>
    <!-- make HTML the default namespace for some commentary -->
    <p xmlns="http://www.w3.org/1999/xhtml">
          This is a 
      <i>funny</i> book!
      
    </p>
  </notes>
</book>