title: How to use "root" namespace of php?
body: <p>I have an Exception class:</p>
  
  <pre><code>namespace abc;
  
  class AbcException extends Exception {
  // blah blah
  }
  </code></pre>
  
  <p>It produces this error: </p>
  
  <pre><code>Class 'abc\Exception' not found ...
  </code></pre>
  
  <p>Questions: </p>
  
  <ol>
  <li><p>What can I do to make this work ? </p></li>
  <li><p>Useful documents are appreciated.</p></li>
  </ol>
  
  <p>Thanks for reading my question</p>