title: Is the XML declaration node mandatory?
body: <p>I had a discussion with a colleague of mine about the XML declaration node (I'm talking about this => <code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;</code>).</p>
  
  <p>I believe that for something to be called "valid XML", it requires a XML declaration node.</p>
  
  <p>My colleague states that the XML declaration node is optionnal, since the default encoding is UTF-8 and the version is always <code>1.0</code>. This make sense, but what does the standard says ?</p>
  
  <p>In short, given the following file:</p>
  
  <pre><code>&lt;books&gt;
    &lt;book id="1"&gt;&lt;title&gt;Title&lt;/title&gt;&lt;/book&gt;
  &lt;/book&gt;
  </code></pre>
  
  <p>Can we say that:</p>
  
  <ol>
  <li>It is valid XML ?</li>
  <li>It is a valid XML node ?</li>
  <li>It is a valid XML document ?</li>
  </ol>
  
  <p>Thank you very much.</p>